Ideas for parking near m5 north Bristol?

[jkh112]

Next week I need to drive up North and will be sharing the journey with a work colleague. He lives in Bath, I live south of Bristol near the M5.
He has suggested meeting at Michaelwood services, where I could leave my car all day. I have 2 reservations about this, will my car be safe and also I will need to drive up to the next junction North of the services before I would be able to gain access to the southbound carriageway.
Anybody got any suggestions as to better places to meet and leave one of the cars?

[GlenMH]

Bristol Parkway station - security is not bad and parking should be cheaper than micheal wood services.
Or the Mall at Cribbs?

[spaximus]

lots leave their cars in the layby at junction 14 just before the services. Not heard of any problems there.