Thanks for your replies

It sounds as if you may be a newish owner?Huh? you probably are being overly cautious and anxious, but it is very good to take care and find out...so keep observing
Yes I'm very new to horses. And yes i'm probably being overly cautious (neurotic?

), but better that than not cautious enough I think.
1. has your pony just had shoes removed and therefore is newly 'barefoot'?
Not had shoes anytime recently I don't think, But her previous owner kept her as a broodmare so I guess she didn't walk out much before (although I'm told she's been broken for riding/driving).
2. what breed of pony is it?
Shetland
3. has your farrier said, for example, that he/she has flat feet?
He didn't make any comment on her feet - just trimmed them - when I get though to him I'll ask him if he noticed anything amiss - but I assumed he would have said when he was here.
4. Is it 'feeling' the hard ground or is it when the ground is stoney?
7. are you in an area where the ground is very hard and dry, even in the pony's grazing field?
It's not a problem in her paddock, but I've been walking her for exercise, and part of the route is on the road (tarmac with loose gravel). Initially she would set off at a trot, but if we stay on the hard surface for any length of time she slows to a walk. If I then move onto the verge she'll happily speed up again. I'm not sure if she's distinguishing between 'hard' and 'stoney' ground - the road inevitably has loose stones on it.
5. does your pony have swollen leg/legs
no
6. Feel the feet, are they hot? ( or is one/two a lot hotter than the others) and if you can find the pulses in the area above the feet...are they really thumping/bounding?
no
part of the reason for the exercise is to keep her weight down - to (hopefully) avoid laminitis. Not that she has any history of such, but I did a lot of reading about shetlands & laminitis and scared myself to death.
It is normal for horses and ponies to prefer softer surfaces if they have the option, especially if they are barefoot, or their legs are tired.
OK so maybe I should be keeping her on the verges then. I just want to be sure I'm not doing anything that's harming her by taking her for walks.
I clean her feet before walking her out and when I get back. I'm currently walking her out every other day; if the ground's been wet, I clean her feet out on the days she's not walked too.