should i get rid of an european sandwich maker 16A 250V?

[Eandyl]

It sounds faulty. Using a 16A product like that on a UK 13A socket will overload it, but you are looking at many minutes for fuses to go, etc, so what you typically see is it works but gradually damages the plug and socket through excess heat.

If it trips immediately that is either a very high fault current (over 3 times the breaker's rating), or it is leaking to earth and tripping the RCD.

Given the cost it is probably not worth bothering with, take a look in places like Argos, Currys, etc, for a UK replacement.

Yes, you are right. If the product trips immediately, it is either a very high fault current or it is flowing to ground.