Well my branch specifically said they don't because "you can't get the new lenses to fit old frames." Whether that is true or not doesn't matter, they wont do it.
There are no independent opticians where I live, so it would be a trip to Edinburgh to find one. The big chains do fine for new prescriptions and I can get a lot of that cost covered by my employer as I have a monitor pair made as well as normal pair. (Bifocals optimised for monitor distance and reading, significantly more comfortable for long periods than my normal varifocals are when using monitors.)