hi all
today as i was driving to work i had a serious loss of power over about 1 mile, it was working very smoothly before now nothing, i cant get above 40 mph and that is all i have. car has done 170k. haven't pushed it over 2.5krpm

car has just had its mot, passed all fine,

coolant and oil level are good

idles fine, no hunting.

looks like a bit of black smoke from the exhaust when driving but only when i put my foot down.

any ideas? any help would be much appreciated