London - Post Office open on Sunday?

Anyone know any post offices open in London on Sundays - the website does not help as I know of a post office that is defiantly open on Sunday and this is not listed as such on the site - I looking for somewhere in the Camden/Tower Hamlets area ideally.

I'm absolutely positive that I used the Post Office in Camden on a Sunday about 4 months ago - but when I phoned up the helpline I was told it does not open on sunday - but they are probably only using the website as a reference.

thanks