I've used P20 and Ultrasun (the highest protection one - 28)
I've also had malignant melanoma.
Ultrasun 28 info from the website:
"Ultrasun 28 delivers very high all day protection (UVA93% and UVB SPF30) with just one application. Its super sensitive formulation is ideal for very sensitive and children?s skins and helps to prevent ?prickly heat? reactions. It provides extra protection for vulnerable areas such as shins, noses, shoulders etc.
It is free from oils, emulsifiers and perfume reducing the risk of allergy and making it especially suitable for sensitive skins. Like other ultrasun products, it is non-staining, non-greasy, water-resistant and easy to use."
P20 offers UVB SPF20 (so lower than Ultrasun) and "some" UVA protection - but I've never found a figure for the level of UVA protection.
UVA causes as much long term damage, so if you want the best protection, I'd go for Ultrasun - I used it last year on a charity cycling trip (6 days in scorching sun, 9 hours a day, sweating lots). I didn't even change colour, which is what I wanted (well, I'd love a tan, but I'm not allowed!)
I've used it on DD (v fair too) and she was fine.
Oh, and I didn't get prickly heat which I always did (badly) when I used P20