I just received an email from P&G after I asked them:
Hello Mr. X and thank you for your email.
Your comments are important to us and I have passed them on to the department concerned.
I am sorry to tell you that we have stopped making Crest, and unfortunately we don't have any stock left.
As a company, we constantly monitor how popular our products are. When the sales of a product fall, we feel it is important to make way for new developments.
We realise that you may be disappointed with our decision to stop making the product, and I hope you will find a suitable alternative soon.
If you would like advice on alternative products, please visit www.oralb.co.uk where you will find our full range of Oral B toothpastes.
I hope this helps but please contact me again if I can offer any further assistance.
So it seems they've moved it over to the "Oral-B" brand instead. Interesting.