Overnight stay?

Stop overnight 380` is a long drive in one hit especially in the UK with the amount of traffic. 

Even for a quick overnight stop?

Some small units have no toilet, Kjell. Are you suggesting a bucket? 

No.  ET has an Eriba, do they not at least have a toilet compartment?

Maybe no shower etc, but absolutely no toilet provision at all must be quite rare these days.

Even the small 2 berth van the in laws had in 1968 had a toilet compartment.

OP has a Lunar Clubman, so does have a toilet.

Yes indeed, here is the Eriba and we have a tiny toilet compartment, and could indeed manage overnight on a site without facilities  - but never in the last 40 years have we chosen to do do so.  Even on sites as rural as this one we expect  to have modern amenities available. That's how we are !

Yes, I can understand that.

Which club site is that, ET? 

KJ, there are still some campervans with no toilets. The bucket was a joke, btw. It's humour. 

T@bs don't have a bathroom. Couple who pitched on same CL as us used a toilet tent. Great for staying on a site, but bit impractical for overnight stop.

Travelling down from W Yorks, I think I'd suggest an overnight stop at Tewkesbury or Malvern. This would give a head start to get through the Bristol/M4junction/Weston super Mare traffic jams if it's weekend holiday travel. Not quite so bad in the week but Bristol rush hour traffic on the M5 can be bad late afternoon. It's about four hours from Tewkesbury to Truro if you're towing.

If you're going to do it in one go, I'd get up very early. 

When we've done that trip from West Yorkshire we've always stopped overnight at Tewksbury. It's very close to the M5.