Is my builder liable for this problem?

[Breathright]

A year ago we had an extension built with a new downstairs bathroom and toilet. For the whole year we've had problems with the toilet blocking and water coming up through the shower. We had the builder back but he said that he did everything in line with the builders reqs and to the right specification, so it wasn't down to him.
We've had plumber after plumber in but the problem wouldn't go away.
Today we had Dyno in and the eventually got to the root of the problem. There was a cement bag stuck three metres down the pipe. He managed to grind through it and clear the drain. In all it's cost me about £300.
Should I try and get that back from the original builder?

 

[Doghouse Riley]

Claim on your house insurance.
Or take it to the small claims court.

Give them the full facts including details of the other people you had in and what they cost.

It's the builder's fault.