P20 is good for application and wear resistance, but be aware that P20 comes in a variety of SPF’s. If you think you can apply a low – medium factor SPF and that’s it for the day, you might be caught out.
Also check the UVA rating, a decent sunscreen should also contain sufficiently high UVA protection (if it does it might have UVA in a little roundel logo). Recent changes also require sunscreens to carry a * rating (0-5) for UVA protection; that’s not an absolute, just a ratio of UVA to UVB protection. Just because a sunscreen has a 5* rating doesn’t mean it has high absolute UVA protection, just that it is a substantial proportion of the overall protection. A low SPF with a high * rating could still have a low absolute UVA factor! Last time i did any market research, P20 only scored 3* on UVA (I’ll look in Boots next time i’m in there)
http://www.bad.org.uk/for-the-public/skin-cancer/sunscreen-fact-sheet#uva-star-system
UVB is the wavelength that causes burns and most surface skin cancers; UVA has been neglected for too long but can cause as much damage in terms of wrinkling, brown spots, etc., and is starting to be also understood as a initiator of skin cancers.
http://www.skincancer.org/prevention/uva-and-uvb/understanding-uva-and-uvb
As a result, my go-to is this
http://www.boots.com/en/Soltan-Once-8-Hour-Sun-Protection-Moisturising-Suncare-Lotion-SPF50-200ml_1207154/
It doesn’t claim the same ‘all day even after swimming’ that P20 does but unless P20 has upgraded its formulation, I’d rather take the inconvenience and reapply after swimming for the extra protection. Also remember P20 won’t survive washing / towelling.
* disclaimer, i don’t work for Boots or any of the sunscreen manufacturers, but my company makes and sells the sunscreen actives to companies like Boots, BDF, Playtex, etc. Hence i know ‘a bit’ about it.