My ford focus is reving high wen i put clutch down and is only doin 40 miles on £10 petrol

This can be caused by a defective Maf sensor and coolant sensor, they will not trigger a code because as long as there is a signal the computer doesn't know the actual engine running condition enough to say the signal from the 2 sensors is wrong, this goes double for MAF sensors, another area is the idle speed control motor.. I want you to read about the problem at the link below.

Ford MAX 2003 2010 03 1 8 Unstable Idle when slowing Technical matters...

does it idle ok when not in gear.

might possibly be caused by the gas cap not on good. try taking the cap off and putting it back on.

the reving can be a vacume leak, Or more commonly idle air controll motor.

Sounds like you need a new clutch. At a stand still put the car in third and try to get it to move. If you don't stall out you need a new clutch.

this may be a problem with the tps sensor

There is a problem with dirty injectors. Please clean those by putting high octane fuel in your car or putting an octane booster in your car also you may lube your cluch look for a valve itatake under the car for that.

high idle choke switch

I am assuming that this is a manual tranny if you have an idiot light. Sounds like you have a clutch that is slipping on you. Put the car on a level surface apply the e brake ,start the car. now put the car in first gaer , don't give it gas and slowly let out the clutch. If the car doen't want to stall out right away as you further let out the clutch or you hear a sliding sount you probably have a slipping clutch. Hope this helps you

take of the fuel sender hose of tank and be prepared to catch any spills wen finshed fill with deisel