Help remembering a title?

[czakal]

Hello everyone,
I'm looking for help trying to remember the title of a children's book that was advertised a lot in the UK. Unfortunately all I remember by now is a description of the cover--it had an illustrated picture of a boy stuck on a sinking boat talking to a fish ('Tell my mum I love her') and the fish replying 'Sorry mate, no signal'?
This is about all the details I remember... not really enough to get anything by web search. Does anyone know the title of that book?

Thanks so much
Sebastien