There are no philatelic counters at Post Office branches as such, and many branches now carry no stocks - with few exceptions - of special stamps. Even Crown Offices often have very small supplies sent to them, maybe one sheet of each certainly of the airmail values in a set.
The principal source for collectors is now Broadway Post Office. The details below were provided in 2018 on the closure of Trafalgar Square PO. I understand that a full range of philatelic material is now available at this branch. The opening hours remain the same. 
Not included in the results, even if you use its own postcode is The City of London PO at 12 Eastcheap, London, EC3M 1AJ but I am told that this has a limited philatelic service - for example they had all four country definitives not just in presentation packs but in sheets.
This office is open Monday - Friday until-1800 with opening hours from 0830 (W/Th/F) to 0930 (Tues) and 0900 Monday.
Update 27 October from Comments:
For Visitors to West London, Leeland Road Post Office in West Ealing stock collectable stamps in all values, I've purchased some stamps of all 2022 issues from here.
NOTE: If you are making a comment about London or other branches' holdings of philatelic stocks it would be helpful to know where they are. I realise that this might jeopardise your own purchases(!), but an approximate location (London, Dorset, Gwynedd, etc) would help others nearby to ask questions - and if you do leave a name or pseudonym instead of 'anonymous' it would help separate the comments.
Our local post office does a lot of the FDCs for locals, and they use the spare stamps from those on drop and go post after they have finished with the FDCs. I don't think they sell them, though.
ReplyDeleteMy Local Post Office Store sill receive a supply of Stamps M/Sheets and blank F.D.Covers I think I am the only Customer these days!., most other PO's in the area don't get any at all, ! & Paignton Main Office get a small Supply of them. RW
ReplyDeleteAttended said PO today to get Aardman Collectors Sheet. Plenty in stock. Enquired about the Christmas Collectors sheet and was informed that they had surprisingly been sent just one (1) sheet, which I was shown. They will order more if requested, so don't bank on any more arriving before 3rd November or it could be a fruitless journey
ReplyDeleteMy local office in Blackheath Village SE3 is great and they try to have the stamps on the first day. They run out quickly but they are really helpful and supportive despite being a bit of a WH Smith franchise these days.
ReplyDeleteI'm down the hill at Lee Green - the sub PO there usually has stuff on on day of issue and will order happily. The son of the postmaster is a stamp fan!
DeleteWent to Gravesend post office in Asda the day after the Aardman stamps came out and managed to get a dozen 2nd Class ones.And the shopping...
DeleteFor Visitors to West London, Leeland Road Post Office in West Ealing stock collectable stamps in all values, I've purchased some stamps of all 2022 issues from here.
ReplyDeleteThank you, that will be useful to some, I'm sure
DeleteUnimpressed by the insipid Xmas stamps I went to Dartford (WH Smith's) this time and sought some more Aardman stamps for Xmas post to abroad. To my surprise they had plenty of stock of them all including presentation packs and miniature sheets. My elation was dampened when they had no 50p make-up stamps though, which is what I had gone in for.
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