That is correct the roof will not open with the key on but you should not have your hands in or fooling with the hyd system with the ignition on for safety reasons.

Opening any of the hyd lines with pressure behind it could cause you harm and you should use caution when doing that.

Thank you all very much for your help in the end I resorted to force as suggested by Oyster and having forced the top up I could see that the hook had gone down onto the latch.Managed to get the latch up and then put the hood down on it and used the allen key as suggested. The windows came up, turned the petcock back, touched the switch the hood went down and all was well with the world.Hood been up and down a couple of times and off now to get some more fluid to top it up.No sign of any leaks under the car or around the headlining.You have all saved me a trip to a dealer and I wont be going back to the Jag specialist I saw yesterday.
Regards
John

Good news.
I'd take the top trim panel off to expose the latch mechanism and lubricate it with your gloop of choice. Some say graphite spray. I just use 3 in 1.
Being agricultural I'm well used to hoses bursting and leaking at far higher pressures than this little tiddly pump can manage and it isn't a life-threatening experience.

Hi John.

That was a relief. I will sleep tight again.
Now, watch that latch "cover" as I mentioned earlier. Be sure it stays down when the latch is coming up to receive the hood hook.
For lubrication I don't know. At least no WD40, gets sticky. Maybe it is best just to keep it clean.

I hear others say that about WD-40 but have not experienced it. You want a lubricant that will not Gel or collect dust and I think this product will do it. It is a dry graphite.

Link CRC Dry Graphite Lube, 16 oz, Net 10 oz - Penetrants and Lubricants - 4JB39|03094 - Grainger Industrial Supply

Just had the same problem, 4 weeks after replacing hydraulic lines. Felt like the latch closed before the top came down and the roof was fully extended except for the last half inch. Could not move it physically after opening petcock. switch neither moved it forward or back and qtr windows were fully down. Disconnected the battery, touched the negative for 30 secs to drain any capacitors and tried again, nothing happened. After a couple of hours, started the car, pushed the button down and the roof came down. Not sure how it got fixed, but guessing the bpm somehow reset. Scary - will shoot the latch with crc dry graphite to keep it smooth.