We wish to travel by car to the South of Spain from the Midlands UK what accommodation is available en-route?

Formula One motels run by Accor. Good basic accommodation at 拢21 per room per night.
Take flip flops! If you want your own shower though upgrade to an Accor.

get ur self a tent

Youth hostals. Many have family rooms and other things that you might need. Cheapest way to travel. Just go on line and look them up. Another way is to vist your local youth hostal in the UK and they can help with your travel plans. Good luck and have fun!

http://www.yha.org.uk/

You'll be driving through France, right? If you're budget concerned consider FormulaOne or Premier Class chains or local B&Bs ("gites"). Don't know much about Spain accomodations, sorry.

It really does depend on the route you take, either driving down through France or via the ferry UK to northern Spain?
We did the latter, had a wonderful over-night trip on the ferry, Plymouth to Santander, landed about 11am, drove south to Madrid & stayed at a lovely hotel just south of Madrid, room cost 50 Euro's for the night & they even let us take our dog into the room with us!