Motorway service stations are a reliable place to park usually but some are tighter than others to get around. Hope this helps.

M1 Motorway.

Wooley Edge.
Northbound. Space in the car park but there are also places marked for caravans.
Southbound. Space in car park.
Woodall. Northbound slightly smaller than others.
Leicester Forest East. Southbound shorter MH in car park. Longer in HGV park.

M40 Motorway.

Cherwell Valley. Dedicated area for caravans. Follow caravan and coach signs.

M42 Motorway.

Hopwood Park. Very large car park with spaces at the top for MH.
Tamworth - Don't go in lorry park especially midweek. Very crowded. Go into cp and on left you can reverse up to trees.

M5 Motorway

Michaelwood - Spaces for caravans both carriageways.

M6 Motorway.

Keale. Room in car park. Stay away from lorry park.
Killington Lakes. Southbound has large car park. Turn left opposite main car park for extra park which has plenty of room for MH.
Sandbach. Both north and southbound have long layby just in the entrance on left. Ideal for motorhomes/caravans but lorries use it as well.

M6 Toll

Norton Canes. Westbound. Dedicated parking for caravans.

M60 Toll Services

Serve both East and West bound traffic. PB

A1(M) Motorway.

Wetherby. Place for caravans and also room in the car park.

M74 Motorway.

Cairn Lodge. Southbound. Good MH and caravan lane just before fuel.
Gretna. Southbound. Separate caravan parking area.