I think the problem with the Charity shops increasing their prices is that it pushes people towards buying cheap imported clothing which may have dubious origins of manufacturing. If people are going into a charity shop and they know they can get an item new from Primark for the same price of course most will do just that!
I think it is a real shame as they are affecting their business and probably turning people away who might have become lifelong customers, there is also the opportunity to find something a little bit different that may no longer be on sale elsewhere. My mother in law works in such a shop and often tells me they check value of items against eBay now to make sure they get the best prices. While I understand they need to make a profit as they have over heads same as any other store, they are not the same, they sell used items and I feel the prices should continue to reflect that fact.
The mail has an article about this here and although it is discussing an upmarket area I feel this is something that is perhaps happening everywhere. A look around the forums seems to show a trend for this topic.
I have mentioned before that some of my bargains have been bought from the charity shop sale, is this what is happening we have to wait for the charity shops to have a sale before their prices are reasonable.
When we are away on holiday in England I often browse a number of charity shops and I think the most reasonable ones are the lesser known ones. I found a lovely wildlife rescue shop in Western Super-mare on a little side street and bought all sorts last year, my husband picked up some CD's, I got clothes, books and belts and I have to say the staff were really helpful. If that shop was in my town I would be a regular.