Thinking of a Caterham kit and would like at least around 140BHP+ Premier Power do a 155BHP Sigma (can't stretch to the 175, too much for me), are there any other options or companies, just wanted to check it all out. Will be for touring and didn't find the 125BHP that pokey. Needs to be new to avoid IVA issues and Q plate... Thanks

What sort of budget are you thinking of for this?

As an example you could source a new 2.0 Duratec for <£2050 from the like of Race Line and install a Webcon Alpha PRO4 (K24001) Gold kit which will give you good power/torque and drivability with the minimum of fuss.
http://www.webcon.co.uk/Downloads/Duratec%20Flyer.pdf