I also used to use P20. It worked very well indeed, but be careful using it as it only prevents sun burn by blocking UVB. When I used it it let the UVA rays through and that is how you tan without burning. It's the UVA that reacts with melanin in the skin to change colour. But this causes ageing and worse. As far as I am aware P20 just stops the painful and damaging burns and blistering of the skin caused by too much sun, which can be dangerous and very painful. UVB can cause immediate damage which can put you in hospital. UVA causes long term damage which can put you in hospital.
Sorry if I am preaching to the converted, but just in case any readers don't know the difference. Unless P20 has changed the formulation in the last 10 years, it stops the UVB only. I suspect Ultra sun contains the same skin "binding" ingredient that P20 has, but only has a bog standard UVA filter, which is what the daily mail dermatologist must have meant.
The skin binding technology in P20 does work for several hours against sunburn but ONLY if it is applied to clean dry skin with nothing underneath, that you wait for 45 minutes before getting dressed after applying and that you do not rub your skin with a towel after swimming.