can someone confirm this is an adder?

Hi Craig

Definitely an Adder. Asp is strictly speaking the name of a different viper species not found in the UK, but does have some usage in the UK. This one actually looks to be about 2 feet long, which is about normal for a BIG male. Females will get up to abut 2.5 feet long.
Where there is one, there are probably more. But I certainly wouldn't worry about them - you were probably quite lucky to find one just sitting there. At the beginning and end of the season this is more likely as they have to work harder at basking!
Actually a beautiful snake that NEVER attacks people - or even dogs - but will defend itself if interfered with. But, when walking where adders are found, wisdom dictates keeping dogs on a (short) lead and wearing decent shoes/boots and long trousers. Actually, unless you stick to well cleared paths, sneaky brambles, gorse and nettles amongst other things, dictate this as sensible wear anyway!
Chris

Hi Craig
An interesting question. Certainly adders have been kept by some people and some do get used to handling. Occasionally even wild ones will accept handling - but only the most stupid would literally handle wild or captive without heavy protective gloves (and even then people have been bitten in unprotected areas - the voice of experience!)
Quite honestly, even if one has a DWA license and excellent facilites these aren't really an animal suited to captivity other than in large outdoor vivaria - where handling would be a rarity.
In short, no-one should handle adders, or indeed, most reptiles just for fun. Very few such animals actually take pleasure in it - and plenty of people have been bitten even by non-venomous constrictors.
Chris