The simplest thing would be to fly back to UK, get it at the Embassy there, and then come back.
Yes, I think it's the easiest way. That's fair enough that Polish Government is being overcautious at that point. When they issue you a visa of different country they take some responsibility upon themselves.
Has any other British / English (or EU members) had experience or difficulty with getting a Russian VISA in Poland or another foreign country??
I don't know about EU members but as for Americans they usually have no problem at all while applying for Russian visa (it's much easier than to get american visa for Russian citizen). You may also reduce the time of getting it if pay. I hope this helps you a bit.
If you need any more info you think I could help you with, don't hesitate to ask. :)