I used to have one of these things in my house when stationed in Scotland in the late 70s. It took 5 pence/shillings and I forget how much gas I got from a single coin. This created a big problem during the very cold winter of 77-78, because the coin box was a finite size and could only hold so many coins.

Between a strike by the British gas workers and my non-conventional work hours, the thing never got emptied. It got to the point where I could not buy any more gas because the mechanism was jammed up. Calls to the gas company were ignored. The situation was resolved by an official complaint through the base and somebody showed up by appointment to empty the thing. The coin box was so full it would not slide out of the housing and the guy ended up bending it so enough coins could be scraped out to permit removal. Since he couldn’t put the coin box back in, he made me promise not to take any coins away after putting them in the machine. I got a whole new meter in the spring when the strike was over, and yes, there was a pile of coins waiting for them.

I remember one well, and it was only 40 years ago. While on vacation in Penzance Cornwall in 1973, the flat we rented had one. It accepted the new 10P coins or the old Florins that coexisted in circulation. I don't recall how much time you got for your 10p or 2 bob, but it was wise to have a stack of them handy for fear of running out in the middle of your cooked dinner or shower. To put things in perspective, the farmers market in town charged 5p (1/-) for a head of lettuce that he went out back to pull out of the garden. We pay about $2.00 for a head of lettuce today making the few minutes of gas we bought worth today about $4.00

Gas and electricity meters were quite common in the UK when I was a boy, particularly, as you say, in multiply-occupied premises. The shilling was the standard coin used for the purpose, and I can remember visiting some friends in the mid-1960s to find them quite concerned about having got two shilling coins wedged alongside each other in the slot, thus potentially running them out of power without the means of being able, without an engineer's visit, to do anything about it.

Some early power meters were not as sophisticated as current slot machines at being able to detect unauthorised substitutes for the correct coin, and I am told that it was possible to freeze water to the shape of the relevant coin and use the resulting discs instead. This had the advantage that the evidence of the misdemanour evaporated, and the disadvantage of rusting up the machine.

The German two pfennig was a very useful substitute for the sixpence at one time, before machines became weight sensitive, but I am not sure what foreign coin was usually favoured in lieu of the shilling. My father's uncle {b.1902} worked for many years for the Cardiff Gas Company and he once said that they had 500,000 cut down British halfpennies in their vaults, all mutilated so as to imitate shillings, which it was not economically viable to shift and scrap. I once heard on the radio that the one county of Glamorgan produced 45% of all the mutilated currency of the UK {Cardiff being its major city}.

His machine accepted a coin and then dispensed a fixed amount of holy water. When the coin was deposited, it fell upon a pan attached to a lever. The lever opened up a valve which let some water flow out. The pan continued to tilt with the weight of the coin until it fell off, at which point a counter-weight would snap the lever back up and turn off the valve.