The cause of which was what in the end ?
Ahh, well, this
particular issue was due to the pipe having "come adrift", while we were wrestling with the LPG wiring, no doubt

. Judging by the whooshing noises coming from it when underway I don't think there is another issue.
How much has it cost in total? A nice break-down of costs would be brill
James already had the tank from a breaker. The kit from Jeremy contained everything we needed for the front end and fuel plumbing to the rear down to the last hose clip. We had to buy a union to connect it to James' tank, which is fair enough. He didn't supply the tank. That and a new LPG filler was about 50 quid from the local LPG guy.
The one thing I would do differently next time is to ditch the piggy back wiring for the petrol injectors and make up a plug and socket on the LPG loom to mate with the multi-way plug and socket behind the 2,4,6 bank, because it was a bit of a struggle fitting all the piggy back connectors under the plenum and there was miles of spare cable on the LPG kit loom.
I'll let James provide the grand total as I didn't pay it but suffice to say that the front end will only need pennies spending on it once you have the kit. Back end depends on choice of tank. Probably another 200-300 quid if you buy new.
Kevin