The Top 30 British brands on twitter by number of followers

"1. Topshop @Topshop_Tweets (99,852 followers)
2. Burberry @burberry (64,128)
3. ASOS  @ASOS (56,838)
4. Comparethemeerkat.com with Aleksandr Orlov (Comparethemarket.com) @Aleksandr_Orlov (41,356)
5. O2 @O2 (31,270)
6. Innocent Drinks @innocentdrinks (30,952)
7. British Airways @British_Airways (24,374)
8. Virgin Atlantic @VirginAtlantic (18,050)
9. Selfridges @Selfridges (17,752)
10. Vodafone  @vodafoneuk (16,842)
11. Nando’s @Nandos_Official (15,732)
12. Heathrow Airport @heathrowairport (14,971)
13. Virgin Media @VirginMedia (14,422)
14. New Look @NewLookFashion (13,040)
15. Westfield London @westfieldlondon (11,404)
16. Lovefilm.com @lovefilm (11,217)
17. Dell Small Business News @DellSMBnews (10,699)
18. Topman @topmanuk (9,299)
19. Samsung @samsungukmobile (8,698)
20. Asda @asda (8,114)
21. H&M @hmunitedkingdom (7,688)
22. Harvey Nichols @harvey_nichols (7,461)
23. T Mobile @tmobileofficial (6,687)
24. Cath Kidston @cath_kidston (6,393)
25. Skittles @skittles (6,168)
26. Honda @honda_uk (5,570)
27. Sony Ericsson @sonyericssonuk (5,259)
28. Dorothy Perkins @dorothy_perkins (4,948)
29. Sage @sageuk (4,717)
30. Waitrose @waitroseuk (4,538)
Source:  compiled by Sutro Digital, 25th October 2010
[Note - these are global followers of companies with either a mainly British presence, British branches of global companies, or thought of as British]
See their site for any corrections and updates!