Also, I understand that if you die before retirement you can't leave all of your pension pot in heredity?
I'm not sure what you mean by "leave all of your pension pot in heredity".
If you die
before retirement you can leave your pension pot by Will (or according to the intestacy rules, if you haven't made a Will) in the normal way and it will be liable to inheritance tax in the normal way.
However, you can write your pension policy 'in trust' and it is usual to do so. If you have done that:-
a) it is no longer part of your estate, so it is free from inheritance tax, but
b) because it is in trust it is no longer your property to give away by Will but will be transferred by the fund trustees according to your previous written wishes. [Writing a pension in trust is just a matter of filling in the pension fund's form and usually free.]
NB The rules about what happens to the undrawn part of your pension if you die
after starting to draw it are not the same.
It's a pity that people's eyes glaze over about pensions, because it really is important stuff. And if they did give it the attention it deserves, the industry would never be able to get away with the outrageous charges and miserable performance that generally applies.