The book "Mosquito" by Sharp and Bowyer contains, on pages 270 and 271, details of the installation of a six pounder gun and it's tests.
I'm sure that I've read, in the autobiography of someone who flew a Tsetse Mossie, that firing the gun set up such a recoil that it was like flying into a brick wall. That, curiously, differs from the tests, mentioned above, that report - " no difficulties with blast or recoil were encountered". If I can find the book I'll post more but don't hold your breath !