Bottle jack with pressure guage port in the UK?

That's probably what I'll try ultimately :-) There are guides on how to do it online, I just would have preferred a commercially available solution for simplicity.

In any case I'm now in a position to experiment and test the viability of the project. If it turns out well then even the cost of a hydraulic pump and ram would be well worth it (8 uses would recoup the cost!).
If anyone is interested the diagram I found is here:
http://www.free-instruction-manuals..../p47111365.pdf
That safety valve does look tempting :-)

Do you actually need to measure directly the pressure inside of the bottle jack or do you need to measure the pressure it is exerting on the work piece or the the gap between the head of the bottle jack and what you are forcing it against?
A pressure pad or similar on the external plate could measure that, or a linear encoder depending on what you really want to measure and bottle jacks van be gotten quite cheaply from xtools.co.uk

D.C., Thanks for the help and sorry for the delay in replying, I've been busy and ill :-)

I actually want to obtain the force, in PSI, applied to a board between two plates pressed together by the jack.

Normally the way this is done is by obtaining the pressure exerted on the ram and calculating the force on the board from the CSAs of the ram and board (and possibly return spring but I don't know if this will be significant until I experiment a bit).
There are several ways of doing it, but I was hoping to keep the ram/pressure sensor part under £70 because I know that this should be achievable (i.e. I can get a sensor for £25 and I know there are jacks with ports out there for around £30 quid I just can't get them to me for less than £70 :-) but there's always the DIY tap option so the < £70 is still viable).

BTW, I'm 90% sure that someone here has found me a hydraulic press with gauge tap for about the price I was hoping for :-)

Anyway, I hope everyone had a Merry Christmas and I wish you all Great New Year!