I´m partly freelancing as a CL300 captain and my rate is 600€/day plus expenses and perdiem (german fiscal rates). BUT I´m not from the UK and 600€ is on the cheap side. (and I do only a littlebit of freelancing these days)
There are not many 300er crew around, since Bombardier CTC and FSI are booked to the brim.
A copilot should get around 450€ / day IMO.
But again, that is for the continent, might need to be beefed up a bit for the UK.