I'd buy a larger quantity of proper 2 part adhesive - several of the trade members on here can supply (Henshaws, Tidel, Rib Shop, etc.).
Will cost more than whatever you might find in B&Q, but does become a lot cheaper buying in a larger quantity (1l, 5l, etc) than buying 250ml at a time!
And I'd certainly use 2 part glue, it gives a much stronger bond. I reseated the floor valve on our Avon Redcrest with 1 part a while back, and it only lasted a year or so before it started lifting. Took it all off again and reseated with Bostik 2402, and it's now solid as a rock!