It happened to me in July 2010 as well. I remember standing in a small British model railway shop in Eastbourne , being ready to pay a sum of GBP 32,50. I had two old type 20pound notes with me, handed them over and received an: "They are not valid anymore. Since July 1st you can only pay with the new ones. But there is a bank up the road, they`ll change there." (I wanted to pay on July 4th

) Fortunately, I had some other notes ith me and paid. Then, I went into the small bank (NatWest) said to the woman at the counter "I heard, these notes are not valid anymore...", gave them to her and received new ones, without any problems. I was not asked whether I had a bank account, nothing.
Maybe this has changed, but I did not have any problems.