If your kids are into Hot Wheels this Big City Gravity Loop is a bargain version of their looping tracks, and it's a fraction of the price at just £6. It was priced at £15 but is now less than half price in the clearance at ELC.
My kids had this track last year, and I think it was well worth the money. It has one big loop on the track, and an adjustable ramp to fly off at the end.
The top end of the track attaches to a table top (or we sometimes used the bookshelves) so you can adjust the height of the track start as well as the angle of the ramp at the end.
It comes with one car included, and it's a standard size so you can whizz Hot Wheels and similar cars down it too. We found that some of the heavier Hot Wheels ones struggled to make it round the loop, but the kids had great fun trying out every car they had to see which ones worked best!
Click and collect is free of charge. Home delivery costs from £3.95 or it's free on orders over £40.