Steve for dear sake go and get a £10 trolley jack from a motor factors or some place and don't be chancing your arm with that piddly jack. that's just plain dangerous. I've seen the results
If you poke any holes let me know Must sort that door soon to.
Hmm i'm concerned! what have you had happen? Ive allways used axle stands if im going under the car, but i would hope the jack is ok. I think theyre pretty good jacks tbh. quick and easy to use.