The longest run we do regularly
Stansted is around 140 miles from Brockenhurst and takes roughly two and a half hours in clear conditions. The route goes M27 to M3, then anticlockwise around the western and northern arc of the M25 before turning up the M11.
That M25 section is the whole story of this journey. It crosses the Heathrow, M40 and M1 interchanges in sequence, any one of which can add twenty minutes in the morning. For an early departure we normally suggest leaving four hours ahead rather than the three that the mileage alone would imply.