The following is a list of the ladybird species that I have seen in the UK.

01 7-spot c.1975 Umberleigh, Devon 1

02 2-spot c.1984 Hatfield, Herts 1

03 22-spot c.1987 St. Albans, Herts 1

04 Orange 01/04/1999 West Putford, Devon 1

05 14-spot 04/05/2000 West Putford, Devon 1

06 Harlequin 30/10/2006 Nazeing, Essex 1

07 Kidney-spot 18/09/2008 Broxbourne, Herts 1

08 Pine 15/05/2009 Chingford, Essex 1

09 16-spot 04/05/2010 Upshire, Essex 1

10 10-spot 10/05/2010 Sawbridgeworth, Herts 1

11 24-spot 20/07/2010 Upshire, Essex 1

12 Red-flanked 20/08/2010 Chingford, Essex 1

13 Cream-spot 08/09/2010 Broxbourne, Herts 1

14 Meadow 22/09/2010 Chingford, Essex 1

15 Adonis 11/10/2010 Nazeing, Essex 1

16 Conifer 07/05/2012 Fishers Green, Essex 1

17 Water 10/05/2012 Fishers Green, Essex 1

18 Red Marsh 10/05/2012 Fishers Green, Essex 1

19 Larch 29/05/2012 Upshire, Essex 1

20 Cream-streaked 30/05/2012 Thundridge, Essex 1

21 Epaulet 05/06/2012 Upshire, Essex 1

22 Eyed 17/06/2012 Upshire, Essex 1

23 Spotted Marsh 18/06/2012 Fishers Green, Essex 1

24 Bryony 09/09/2012 RSPB Rainham, Essex 1

25 Ivy 12/09/2012 Broxbourne, Herts 1

26 Heather 13/03/2013 Nazeing, Essex 2

27 Red-headed 27/03/2013 Nazeing, Essex 1

28 Dot 19/09/2013 Nazeing, Essex 1

29 11-spot 14/05/2014 Cudmore Grove CP, Essex 2

30 18-spot 15/08/2014 Church Hill, Herts 2

31 Oak 28/06/2015 Fishers Green, Essex 5

32 Scarce 7-spot 22/08/2015 Esher Common, Surrey 5

33 Striped 22/08/2015 Esher Common, Surrey 1

34 Heath 22/08/2015 Esher Common, Surrey 1

35 Hieroglyphic 22/08/2015 Chobham Common, Surrey 1

36 Red-rumped 25/06/2017 Warren Hill, Suffolk 1

37 Angle-spot 03/07/2017 Fen Drayton, Cambs 1

38 Bordered 10/07/2017 Pashford Poor's Fens, Suffolk 1

39 Red-patched 03/08/2017 Nazeing, Essex 1

40 Ant-nest 03/08/2017 May Day Farm, Norfolk 1

41 Forestier's 16/08/2017 Nazeing, Essex 1

42 Dusky 15/07/2018 Waltham Abbey, Essex 1

43 False-spot 22/07/2018 Canvey Wick, Essex 1

44 Black 06/09/2018 Thetford Warren, Norfolk 1

45 Schmidt's 23/08/2019 Grimes Graves, Norfolk 1

46 Horseshoe 07/10/2019 Fishers Green, Essex 1
If recording ladybirds in the SE of England then 30 species seems to be an achievable target.
(My best year list was 34 species in 2017 and I saw 32 species in 2018 and 2019).
Forty species requires a bit more effort, including travelling to find specific target species.
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I have yet to see 13-spot Ladybird (two unsuccessful trips to Sussex) and 5-spot Ladybird (not yet travelled for).
These are my last remaining resident species and would take my list up to 48.
At the moment it seems that a total of 50 species is just out of reach.
However, as more people search for ladybirds, especially in bird migration hotspots and urban habitats, it is quite likely that more newly established species will be found, either as natural migrants or human introductions.