www, yes, P20 is the one-application-lasts-all-day one - put it on 90 mins before exposure and flap about naked until it dries. (NB have never tried it properly myself!) I think you can get it in Superdrug.
Not sure the Sunsense one is the same as P20 does have PABA and Sunsense doesn't - I think it will depend on whether there is an allergy factor. Also Sunsense "bonds" and P20 "binds"!
These are the 2 descriptions:
Sunsense Sport Gel 30 :
Easy to apply, non-greasy gel for sports people.
Cool and dry.
Provides SPF 30 protection even after 6 hours in the water giving water sports enthusiasts the protection they need in and out of the water.
Blocks UV-A and UV-B rays.
Screens infrared and visible light.
Preservative free (contains ethanol).
Does not contain PABA, PABA derivatives or lanolin to reduce the risk of sensitivity reactions to those people who are already sensitive to these ingredients.
SUNSENSE should be applied to clean, dry skin, 15 minutes before exposure to the sun. This allows the sunscreen to bond to the skin.
P20:
The active ingredient in P20 is PABA (p-aminobenzoic acid), which is a natural substance found in the human body, also known as vitamin H. When P20 is applied to the skin the p-aminobenzoic acid is absorbed and binds to the keratin, a process that takes 90 minutes. After this binding, P20 gives long-lasting and effective protection.
Amazingly P20 lets you tan! It gives high protection (SPF20) against the sun's "burning" UVB rays, but still lets through some UVA rays to allow you to tan. Result? A golden tan without "the burn". Remember the sun is at its strongest and should be avoided between 11am and 3pm.
P20 is non-greasy and fragrance-free once dry, so you no longer have to apply sticky sun preparations throughout the day! Because of this it is ideal for men with thinning hair as there is no grease or "shine" like normal sun preparations. Remember not to use any moistuiser etc, before using P20 as it will stop the product binding to the keratin of your skin.
To use, apply P20 each morning in an even layer to clean, dry skin, 90 minutes before sunbathing or swimming, paying particular attention to vulnerable areas such as the face, shoulders, shins and feet.
Because P20 is different, full directions must be read carefully before use.