I had a builder do work in my house in 2010 to the value of 7700, the builder is now under investigation by revenue / cab, the builder got me to sign a form stating that he did in fact carry out this work, but yesterday I received a call from the builders solicitor telling me I had to be in court on Friday to give evidence, my question is do I have to be there?

Have you actually been petitioned by the court to appear? I don't think you have to appear on the solicitor's request alone. They have your letter confirming he did the work which should be enough.

Normally the court will issue a summons to appear as a witness. If this is a hearing of some type and not court, it may not be that way. I guess the question is, do you want to go help them, or not. Are they willing to pay your loss work if you do ?