After getting my floatplane rating in Canada a few years back I did look into what would be involved in renewing said rating with the CAA. I eventually decided that flying mainly from Barton EGCB, there was little likelihood of landing on the Manchester Ship Canal so I gave up the idea.
But I did get as far as getting the recommended Royal Yacht Association books because to keep a floatplane rating in the UK it is necessary to know the light signals shown by a dredger operating at night!