Well retinol is available OTC here, for under a pound a tube, at a reasonable percentage of active ingredient. If you wanted a retinol containing product in the UK, I think you'd need Vichy or ROC or something. Retinol products don't tend to come cheap in England and they don't have much actual retinol in them as above a certain percentage it's a pharmaceutical product. It has anti-aging and anti-acne effects; what it does is speed up cell reproduction in your skin. It does dry your skin out or make it flake off a bit though, especially in fragile areas. I dunno if it would be a problem with your sensitive, allergic skin? On the other hand, it makes things heal really quickly.
I mixed it with my moisturizer for the first few weeks, then used it neat every three days, then built up until I was using it every day to avoid massive skin irritation, but the skin around the corners of my mouth is still very flaky.
My step-mum buys it off ebay or amazon or something from Thailand.