Depends where in London
300s are at Blackbushe and Biggin / Rochester with Cabair.
R44s at Redhill with LHC and EBG, Denham Heli Air, Elstree (I Think) Cabair, Damyns Hall Helicentre, and at Rotorvation Nr Brands.
And if they still train on it the Bell 47 at Alan Mann at Fairoaks (no idea of seat limit but I'd bet you are ok).
Next step up is Bell 206 and EC120 also at some of these locations.
GS