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 can handle both, but some appliances can't!
Another option is to buy a replacement power supply which has the correct output voltage, polarity & connector and can handle a 2A current draw. Amazon sell plenty of 12v 2A power supplies such as this example https://www.amazon.co.uk/JnDeeTM-Quality-ADAPTER-Transformer-TRANSFORMER/dp/B00ENZUQO8
All of this information is marked on your existing adapter, notice:
- OUTPUT 12V 2000mA
- DC power
- centre positive
What isn't marked is the plug diameter.