Unfortunately the removable prongs are specific to this adapter. They’re not the same as the removable prongs on a different adapter. So good luck finding the right ones. Perhaps there were a bunch of different prongs in the box when you bought it, and you threw the other ones away. Perhaps they put the right one on at the factory.
However, it is labeled 100-240V 50/60Hz. This adapter will have no trouble running on British electricity… if you can get the right prongs on it.
You are looking for an adapter which lets you plug a US plug into a British socket. It doesn’t have to change the voltage, it just has to change the prongs. Something like this one (a random Google result; I am not endorsing this particular product):
Note: Be careful when plugging things into this adapter, because UK and US electricity are different and this will give you UK electricity with US prongs. This turntable’s adapter (the black one) can handle both, but some appliances can’t!