Where should I live? Criteria are:- Need fast, easy access to London by rail- Want a nice country home in a quiet location (bigger=better)- Budget is £300K or thereabouts- Quick access to M1 and M4 preferred

This is an interesting visualisation. You can adjust travel time and see where the fast trains are; or adjust houseprices at the same time!http://www.mysociety.org/2007/more-travel-maps/From personal experience I would suggest Gerrards Cross/Chalfont area for easy access to M4 and M1. Alternatively Slough and Woking have more frequent trains to London but are quite a way from the M1.

Try St Albans: 18 mins to Kings X and very close to the M1. Plus they're putting in Europes largest urban park shortly and really upgrading the Thameslink over the next 3 yrs.could be as good investment

winchester area

Reading Area. Or if you want a big house for £300k then Swindon area - 1 hour on train.

Milton Keynes, great area, very green, 70mph hour roads right into town and just 34mins to London. housing is cheap too.

Watford believe it or not - less than 20mins direct into London by train, easy by road, is within M25 and has lots of green country suburbs, big houses/flats for a lot less money than anywhere within M25, is on the M1 and a quick 20mins round the M25 to the M4

Some of the suggested areas (Milton Keynes and Watford in particular) are quite grubby and soulless. Why not look at some of areas near West Hampsted? Great tube links, will benefit from the Thameslink upgrade, and easy access to both M4 and M1. Quite built up, bit within easy access of M4 and M1.