I do not know how your healthcare coverage is in the uk so I cannot answer the cost issue.
Depending on the size of the mole and how it needs to be removed determines whether he/she will remove it right then and there or not.
I know that here in the u.S, insurance will only cover the cost if there is a medical reason for it to be removed. Like, if they think it is cancerous or poses a risk to your health or if it causes pain etc.