| McStones (UK) Ltd dba The Royal Oak dba The Royal Ruchi | | | tax violations | 2020 | UK-HMRC | £118,878 |
| MCT Partnership LLP | | | accounting fraud or deficiencies | 2022 | UK-ICAEW | £350 |
| McWhirter Transport | | | tax violations | 2016 | UK-HMRC | £36,494 |
| MDC High Peak Accountants Limited ASP | | | anti-money-laundering deficiencies | 2022 | UK-HMRC | £3,908 |
| MDIS Construction Ltd | | | tax violations | 2023 | UK-HMRC | £302,577 |
| MDIS Painting Ltd | | | tax violations | 2023 | UK-HMRC | £59,024 |
| MDistribution Limited dba Milano Pizza | | | tax violations | 2019 | UK-HMRC | £179,261 |
| MDM Global Ltd | | | tax violations | 2016 | UK-HMRC | £490,501 |
| Meadowhall Wholesale Ltd dba Meadowhall Cash and Carry | | | tax violations | 2017 | UK-HMRC | £1,379,026 |
| Meadows & Co Limited | | | accounting fraud or deficiencies | 2024 | UK-ICAEW | £1,050 |
| Meadway Estates (North London) Limited EAB | | | anti-money-laundering deficiencies | 2022 | UK-HMRC | £4,500 |
| Med Bar & Grill Limited (Formerly trading as ‘Med Bar & Grill’) | | | tax violations | 2023 | UK-HMRC | £86,843 |
| Media Station Ltd ASP | | | anti-money-laundering deficiencies | 2023 | UK-HMRC | £2,650 |
| Mediterranean Commercial Catering Ltd dba Lemon Tree dba Il Palazzo | | | tax violations | 2019 | UK-HMRC | £121,007 |
| Mediterranean Fish Bar | | | tax violations | 2018 | UK-HMRC | £14,850 |
| Meera Catering Ltd dba Meera Caterers | | | tax violations | 2018 | UK-HMRC | £337,783 |
| Mega Bite | | | tax violations | 2018 | UK-HMRC | £27,260 |
| Mehrab Ltd dba Tava Restaurant | | | tax violations | 2018 | UK-HMRC | £41,646 |
| Mehta & Tengra | | | anti-money-laundering deficiencies | 2015 | UK-ICAEW | £7,505 |
| Melissa Ford - Property Expert Limited EAB | | | anti-money-laundering deficiencies | 2022 | UK-HMRC | £2,700 |
| Mellerstain Developments Ltd | | | tax violations | 2017 | UK-HMRC | £19,600 |
| Melsel Food Limited dba Alex's Cafe Restaurant | | | tax violations | 2020 | UK-HMRC | £71,309 |
| Melton House Investments Ltd | | | tax violations | 2018 | UK-HMRC | £65,288 |
| Menzies LLP | | | accounting fraud or deficiencies | 2019 | UK-ICAEW | £7,080 |
| Menzies LLP | | | accounting fraud or deficiencies | 2023 | UK-ICAEW | £6,000 |
| Mercy Global Consult Ltd | | | tax violations | 2023 | UK-HMRC | £179,810 |
| Merrill Lynch International | Bank of America | financial services | investor protection violation | 2017 | UK-FCA | £34,524,000 |
| Merrill Lynch International | Bank of America | financial services | investor protection violation | 2015 | UK-FCA | £13,285,900 |
| Merthyr Industrial Services Biomass Ltd | | | tax violations | 2018 | UK-HMRC | £31,692 |
| Metis Real Estate Advisors Limited EAB | | | anti-money-laundering deficiencies | 2023 | UK-HMRC | £27,000 |
| Metro Bank plc | Metro Bank PLC | financial services | banking violation | 2020 | UK-CMA | £11,400,000 |
| Metro Bank plc | Metro Bank PLC | financial services | internal controls deficiency | 2021 | UK-PRA | £5,376,000 |
| Metro Bank PLC | Metro Bank PLC | financial services | accounting fraud or deficiencies | 2022 | UK-FCA | £10,002,300 |
| Mett&i Limited | | | tax violations | 2019 | UK-HMRC | £88,463 |
| MG Associates Ltd | | | accounting fraud or deficiencies | 2016 | UK-ICAEW | £14,350 |
| MG Audit Services Ltd | | | accounting fraud or deficiencies | 2017 | UK-ICAEW | £5,000 |
| MG Cars | | | tax violations | 2016 | UK-HMRC | £82,123 |
| MG Group (Professional Services) Ltd | | | accounting fraud or deficiencies | 2018 | UK-ICAEW | £698 |
| MGA Accountants LLP | | | accounting fraud or deficiencies | 2022 | UK-ICAEW | £2,800 |
| MGM Accountancy Ltd | | | tax violations | 2021 | UK-HMRC | £56,603 |
| MGR Weston Kay LLP | | | accounting fraud or deficiencies | 2021 | UK-ICAEW | £2,100 |
| MGR Weston Kay LLP | | | accounting fraud or deficiencies | 2021 | UK-ICAEW | £0 |
| MHA MacIntyre Hudson | | | accounting fraud or deficiencies | 2017 | UK-ICAEW | £16,805 |
| Mi Julies Chippy | | | tax violations | 2014 | UK-HMRC | £48,448 |
| Michael Blench Haulage Ltd | | | tax violations | 2022 | UK-HMRC | £13,650 |
| Michael J Dodden & Co | | | anti-money-laundering deficiencies | 2018 | UK-ICAEW | £7,443 |
| Michaels Drinks Plus Ltd | | | tax violations | 2020 | UK-HMRC | £706,447 |
| Mideast Sat No. 1 | | | tax violations | 2018 | UK-HMRC | £26,873 |
| Midland Construction Management Telecoms Limited | | | tax violations | 2023 | UK-HMRC | £134,091 |
| Midland Steel Services Ltd | | | tax violations | 2020 | UK-HMRC | £34,635 |
| Midnight Cafe Ltd dba Flames | | | tax violations | 2019 | UK-HMRC | £20,269 |
| Mike Clark Book-Keeping Services Limited ASP | | | anti-money-laundering deficiencies | 2023 | UK-HMRC | £2,500 |
| Mike Phillips Transport Limited | | | tax violations | 2020 | UK-HMRC | £24,690 |
| Mil Logistics Services Ltd | | | tax violations | 2018 | UK-HMRC | £78,941 |
| Miles Byron Ltd EAB | | | anti-money-laundering deficiencies | 2023 | UK-HMRC | £1,750 |
| Miles Hutchinson & Lithgow | | | anti-money-laundering deficiencies | 2023 | UK-SRA | £3,203 |
| Milesforless Ltd | | | tax violations | 2023 | UK-HMRC | £33,294 |
| Military House Limited | | | accounting fraud or deficiencies | 2021 | UK-ICAEW | £3,258 |
| Millburn Insurance Company Limited | | | internal controls deficiency | 2016 | UK-PRA | £2,863,066 |
| Milomagro Ltd | | | tax violations | 2024 | UK-HMRC | £93,129 |
| Milton Coach and Mini-Bus Hire | | | tax violations | 2018 | UK-HMRC | £21,772 |
| Minerva AG Cafe Limited dba Minerva Cafe | | | tax violations | 2019 | UK-HMRC | £50,102 |
| Mineworld Limited | | | investor protection violation | 2015 | UK-FCA | £5,000,000 |
| Ming's Happiness | | | tax violations | 2018 | UK-HMRC | £39,681 |
| Minik Ltd | | | tax violations | 2017 | UK-HMRC | £13,551 |
| Mint Innovations (MD) Ltd | | | tax violations | 2017 | UK-HMRC | £18,560 |
| Mirpa Limited HVD | | | anti-money-laundering deficiencies | 2023 | UK-HMRC | £14,500 |
| Mirroman Ltd | | | tax violations | 2023 | UK-HMRC | £1,403,576 |
| Mission Practice Ltd | | | tax violations | 2020 | UK-HMRC | £58,098 |
| Mitchell Glanville Limited | | | accounting fraud or deficiencies | 2020 | UK-ICAEW | £18,587 |
| Mitchells (Derbyshire) Limited | | | accounting fraud or deficiencies | 2018 | UK-ICAEW | £3,800 |
| MITU Carpentry & Joinery Ltd | | | tax violations | 2022 | UK-HMRC | £84,076 |
| MJB Business Services Ltd ASP | | | anti-money-laundering deficiencies | 2023 | UK-HMRC | £2,750 |
| MJB Scheme | | | tax violations | 2017 | UK-HMRC | £47,192 |
| MJI Construction Limited | | | tax violations | 2019 | UK-HMRC | £23,672 |
| MJT Citrix Consultancy Limited | | | tax violations | 2023 | UK-HMRC | £24,849 |
| MK18 Limited ASP | | | anti-money-laundering deficiencies | 2022 | UK-HMRC | £6,400 |
| MM Builders Ltd | | | tax violations | 2023 | UK-HMRC | £190,457 |
| MM Swansea Ltd dba Mini Masala | | | tax violations | 2018 | UK-HMRC | £36,960 |
| MMA Financial Management Limited ASP | | | anti-money-laundering deficiencies | 2022 | UK-HMRC | £13,400 |
| MMO Limited | | | anti-money-laundering deficiencies | 2020 | UK-ICAEW | £7,040 |
| MMO Limited | | | accounting fraud or deficiencies | 2022 | UK-ICAEW | £3,450 |
| Mobilezone (UK) Limited | | | tax violations | 2016 | UK-HMRC | £25,466 |
| Modern Living Properties Ltd EAB | | | anti-money-laundering deficiencies | 2023 | UK-HMRC | £14,500 |
| Mojito Lounge Limited (The) dba Blueberry | | | tax violations | 2016 | UK-HMRC | £143,288 |
| Mold Elm Kebab Ltd | | | tax violations | 2023 | UK-HMRC | £113,332 |
| Monarch Commercial Limited EAB | | | anti-money-laundering deficiencies | 2022 | UK-HMRC | £3,500 |
| Moneemint Limited | | | tax violations | 2023 | UK-HMRC | £375,677 |
| Money Movers Ltd | | | anti-money-laundering deficiencies | 2021 | UK-HMRC | £0 |
| Moneywise IFA Limited | | | investor protection violation | 2010 | UK-FSA | £19,600 |
| Monifieth Car Wash | | | tax violations | 2017 | UK-HMRC | £19,057 |
| Monkmoor Bathrooms Ltd | | | tax violations | 2023 | UK-HMRC | £53,689 |
| Mono Manchester Ltd | | | tax violations | 2017 | UK-HMRC | £67,376 |
| Monter Limited | | | tax violations | 2016 | UK-HMRC | £266,766 |
| Montgomery Taff Ltd | | | accounting fraud or deficiencies | 2020 | UK-ICAEW | £350 |
| Montrose Food & Wine Limited | | | tax violations | 2018 | UK-HMRC | £17,156 |
| Mookys Print and Design Ltd | | | tax violations | 2022 | UK-HMRC | £147,923 |
| Moonlight Curtains and Interior Design Limited | | | tax violations | 2018 | UK-HMRC | £20,412 |
| Moonlight Pharmacy Ltd. | | | tax violations | 2016 | UK-HMRC | £18,673 |
| Moore | | | accounting fraud or deficiencies | 2017 | UK-ICAEW | £5,000 |
| Moore Family Office Limited | | | accounting fraud or deficiencies | 2021 | UK-ICAEW | £700 |
