At the moment UK evaluations via SIGNET will only accept pedigree/purebred data however this is set to change. If you want to do it I would say collect all the data and wait 18 months, you should then be able to enter any data from crossbreds
If you are good you will persuade them to enter 2 or 3 years of data for a single years fee (sorry Sam if you are reading this!) So record sires and dams, birth dates and weights, born-- alive and dead, 8 week and 20 week weights and weights of all ewes before they go to the tup ---put it on an excel sheet and save it for a year or so