Your 4-door Astra doesn't fit a baby seat Nikbrad? :-k We have a 2005 Astra hatch as well and ours fits just fine. We did purposely by a 'compact' model of carseat, knowing that many of the plush/fancy models probably wouldn't fit. We have the seat in the middle of the backseat; and it is the IOC Baby GoSafe model (RRP around $170). It's not fancy but it works just fine for Maddy and as both DH & I are quite tall, we still have plenty of leg room in the front seats.