Phil, I don't mean deliberately. To be honest I think the problem is that as people with English accents we need to find that compromise between how we talk and how we sing, because our speaking accents are uniquely mis-suited to singing. That compromise won't always end up with a recognisably-English accent. And as I said in my last post, some of these songs might have been written back when we *were* speaking like Americans. :-)
Lest people misinterpret how I wrote my earlier post, that would be "lah-ah-ahve" for "love". A long-vowel "lahve" for "love" is what Brits would see as a classic example of an American accent. A shorter harder "lav" for "love" is a classic estuary-English accent. Northerners would say something more like "loov" with a short vowel. Neither is well-suited for singing. And singing "lo-o-ove" perfectly on the vowel puts you squarely into the "I-want-to-sing-like-Noel-Coward-let's-all-go-to-elocution-lessons-old-bean" ballpark. More commonly with less-good singers, on longer notes the vowel sound changes as the singer moves through the note. This usually sounds horrible, with some strangled sound like "loh-ah-arve". An alternative to all this of course is the more nasal traditional-folk delivery which often results in something more like "loi-i-ive" - and now we're heading towards an Irish accent.
The letter "i" is another similar problem, in that it's virtually impossible to sing a long "i" without becoming nasal, and most people don't like that kind of sound unless you're consciously aiming for a trad-folk delivery (which again is different from anyone's spoken accent). So "smile" might become "smahle" - again, we're into American vowels again. Phil, to take part of your example, "hiiiigh" is almost universally sung "hah-ah-igh" - American again.
As several people have said earlier, singers usually lose much of their regional accent when they sing. I think it's simply because you *can't* usually sing in those accents! (I'd submit three Geordie nominations of Jimmy Nail, Chris Rea and Mark Knopfler, all of whom are broad Geordie when speaking but not at all when singing.) Where English singers *do* stick with their speaking accent in singing, I think it's very often as part of an act which consciously trades on their regional (or ethnic) background, like Cockney music-hall songs.