Theres a services on A14 at Kettering but small & usually full of trucks. Otherwise go off at J9 A509 exit, take first exit in towards Kettering & a short distance there is a Tesco, large car park plenty of room at back to park with caravan. Look at it on streetview you will see what I mean. Pizza Hut, etc there as well.
Otherwise not a lot except 2 small services until you get to Cambridge services which is large. Although services at A1 junction is probably ok, but full of trucks again.
There are lay-byes all along the A14, some are quite well set back off the road. There are a couple of good ones before you reach the A1 /A14 roundabout. Depends what time of day as they do get the truckers resting in them.
There is a small services on the roundabout at the A45 / A605 junction. Not sure what it is like for caravans, have a look on streetview. (Shell garage and little chef). Stopped there in trailer tent days.
------------- Alan
2016
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