What is the meaning of “one of those shilling in the slot affairs”?

Question

In A Taste Of Honey by Shelagh Delaney I found this:

(She wanders around the room searching for fire.) "Where!" she says. She can never see anything till she falls over it. Now where's it got to? I know I saw it here somewhere . . . one of those shilling in the slot affairs; the landlady pointed it out to me as part of the furniture and fittings.

Is it a metaphor? Does it just mean that it is something that costs money or is there a special meaning?

On the Internet I could find different variations where instead of word shilling were used coins, penny, nickle.

Another example from the Internet:

This park stretches over 1,000sqkm from Torquay to Princetown and boasts numerous picnic and barbeque spots. Some are coin-in-the-slot affairs, others are push button and free of charge, while still others are the old-fashioned kind: strictly BYO fuel.

Answer 1

Need a bit more context really, but I would take it to mean 'purely mechanical'.

Edit: a gas fire, of the metered type that means you put a shilling in the slot and get enough gas to heat the room for a certain time.

Answer 2

Most UK houses nowadays are metered: you have an account with the gas or electric company, they measure how much you use, then bill you, then you pay them.

They're becoming much rarer, but some houses didn't have meters like this, particularly for students' lodgings. Instead, they're an early example of pay-as-you-go (now familiar with mobile phones). When you wanted to use gas or electricity, you would to have to physically put a coin into the meter, just like with a telephone box. Someone from the company would later come and collect the coins.

Before decimalisation in 1971, there were 20 shillings per pound and 12 pence per shilling.

Here's a photo of a 'shilling in the slot' gas meter, from the 1940s or 1950s: