I would reccommend that anyone with a YAK spends some time with Genna, but there are a couple of things you ought to be aware of, just to keep you legal!
If the aircraft is on a UK Permit to Fly it can not be used for aerial work and thus there can be no payments made.
If it is still on a foreign register you need an operating permit (See ANO Article 115). I can't remember if this comes from the CAA or the Department for Transport.
In any case speak to the CAA General Aviation Department who will normally help in obtaining the correct paperwork.
AC&X