Out of what I've seen, the most highly rated older series not released in the UK is 'Now and Then, Here and There.' It clearly didn't do too great in yankland and, eve though it's one of the few 10/10 worthy series I've seen, it'll never see the light of day in the UK. I was lucky to get the sealed R1 box set after it went OOP on eBay...
As for Scrapped Princess, it's a blessing in disguise it wasn't released in the UK by Beez. Would you really want to pay £60 for DVDs with the worst shimmering ever? Unless Beez used the Madman masters, which lessened the shimmering quite a bit, then it'd be a complete waste of money. It's best just to get the cheap Anime Legends set.