my lawn has got thatch, does anyone know how to get rid of it?

Not sure what you mean by 'thatch' are you not removing the grass clippings?

My lawn gets a lot of thatch even though i remove all the clippings. I get rid of mine by scarifying with an electric lawn rake which removes moss as well as the dead grass. You could also use a hand grass rake if you have a small lawn and plenty of muscle! I'm not sure when is the 'corrrect' time to do this, I did mine a couple of months ago but I think late spring is better. A lawn feed after raking encourages the grass to thicken which helps reduce the problem.

Thatch is just dead grass, scarify it in the autumn. Then spike with a garden fork pushing it in and wriggle the fork out, about a foot apart. Then bush in sharp sand.
prune