The amount is less than GBP 325,000, but it's a decent whack.
You misunderstand: the tax is paid by the person who died. It doesn't matter who gets how much, only the size of the estate. If it is over GBP 325,000, there is a 40% tax on the amount over that figure.
The mutual agreement between Poland and UK about the avoidance of double taxation does not pertain the inheritance tax .
And why would it, given that there is no inheritance tax in England, only estate tax? But of course you don't know the difference between the two. Stick to pretending to be a Polish lawyer, Monia.
As suggested I will talk to a professional about this, and also to ukpolska (thanks Polmed).
Speak to ukpolska before you speak to a professional: there may well not be a need to pay for a professional.
a) whether I'm supposed to declare this to the Polish taxman, or how else he might find out?
b) whether leaving the money in the UK, or not bringing it to Poland would exempt me from any possible taxes?
c) If, as a normal UK citizen residing in the UK I would obliged to declare the money and pay tax, or would this tax already have been paid before I got the money?
a) If you bring it here, declare it.
b) Leave it in the UK and there is no tax liability in Poland (there is no tax liability if you bring it to Poland but you do need to declare it).
c) The tax is not owed by you and if there is any due, it will be taken before the money gets to you.