car juddering@ 2000rpm

[mollyhc]

on the way home from the lakes this week the car developed a strange fault.Left the lake district on a full tank got to manchester and had only used just over a 1/4 of tank , then as the rain got worse was happily travelling at 40 as the revs hit 2000 the car would judder as if about to stall, also the fuel economy was dire as i used 3/4 of a tank to get to birmingham and there was a strong smell of fuel.After refuelling at birmingham had a clear road so got the foot down and got all way back to london on 1/4 of tank!.Tried to replicate fault but it seemed to have cleared but as its a tvr it will happen again , any ideas , i thought it was a product of the weather as it was bucketing it down or maybe bad fuel.