Looks like it's separate - or cunning way for Lovefilm to reach a different demographic, maybe; either way, Lidl pointed out its differences in pricing to LoveFilm when it launched last year (news story here).
Lidl is powered by OutNow - who have a lot of bad reports from users - especially in relation to having problems canceling the free trial.
If you want cheap, Tesco is probably the cheapest with a decent service, it's powered by LoveFilm. I used it for years and it always had an incredibly quick turnaround.
There is a review of Lidl here with user ratings and a review. One of the interesting things it says they only have 180 blu-ray titles, which seems pretty low if that's why you're renting http://www.choosedvdrental.co.uk/dvd-rental-review/lidl-movies.asp