clutch slipping mid stroke, scary any advice boys?

[ooopnorth]

just got my 6n its done 78K and has been looked after well with FSH. apparently it had a new clutch fitted last year. when i got it from the nice lady. both the clutch & throttle cable had stretched to such an extent that the 1st 2" of travel on either pedal didn't do anything! ive tightened both up nicely and now the throttle response is crisp and iv got the biting point where it needs to be.

The problem is halfway through the clutch travel the clutch slips and the car jumps forward. it happens more in 1st when trying to hold on the biting point and more when its cold. its making for some scary pulling out moments especially on fast roundabouts. ive tried tightening it right up and it makes the clutch useless. slackening just makes the biting point right near the floor but it still does it.

anybody know what this is??? im getting a bit worried.

cheers boys