Well fitz me hearty, it's not just a bloody concrete lintel (well it is but it isn't if you know what I mean). The lintel represents an affront to various professions and I guess some religious bods as well, and they naturally get a bit upset about that - bit like people getting upset about the bones of their ancestors being on display in a museum.
Don't know the first thing about rock art but I respect you and others who do. Guess when dickheads start defacing rock art you naturally get upset (and I'm with you 100% there). We kinda feel the same way down south, with lintels and time capsules and stuff.
Anyway, get your butt down here sometime soon and I'll bore you speechless with talk of lintels and wells (oh, no, sorry goff''ll do the latter). Also found a great pub last time I was in Avebury called the Who'd Have Thought It - best ham and eggs I've ever had! Reckon we should have a Mini Megameet there before 'summer's' over :-)