If you are going to play the whole year, invest in air. Definuitly get air if you want to use an RT , e-grip or flatline.
You'll need a CO2 bottle with on/off, antisyphon and an expansion chamber , that'll cost about £75. You can pick up used system for just a bit more than that
Lots of sites have started checking if CO2 bottles are UK legal. Some do, some don't but it's really not worth the hassle
buy air instead!