You can take your credit/debit cards and use them to obtain cash at a very reasonable rate.
Only problem we found was that most of the ATM's in the hotels in Pamporovo were out of action last week. There is a Bank with an ATM attached to the Perelik and we used this several times last week without any problems.
You'll have no problems if you take Stirling. 99% of places accept the Pound - even the chaps selling the cow bells - and there are a rediculous amount of places to exchange it for Leva. In fact, you get a slightly better rate in Bulgaria than you do in the UK, even in the heard of the resorts (although you wont make a fortune in trading between the currencies!)
the man on the moon is coming
to nite hope you like the snow
i do i think it is nice
my techer is gowimg soon on holday
so you tell me what you think of
the wether ok
love richard ?
i fly out sat so i left it too late to order but sure at the end of the day money is money so i am fairly sure i will have no problem gettin rid of any currency.