My 11 week old pup has just been stung by a wasp on her lip. I phoned the vet and they said keep an eye on her, but if I'm at all worried, to come in.
She's very subdued and has become sleepy and the lip is swelling a little, what are the more worrying signs to look for?

Having had the (expensive) pest control round to successfully destroy the wasp nests the other day, somewhat peeved to still have wasps around.

I would want to give Piriton to stop the swelling as it's on the mouth.  Ask your Vet for the right dose for your pup.

I did ask about anti hysts as I have them for myself, but the vet nurse said not to and allow the pups own immune system to deal with the sting. However had the sting been further into the mouth or throat then that would be a different matter

Lip swollen more and she is lying in her crate looking thoroughly miserable.

I used to give benelate  or piriton...ie an antihistamine tablet to reduce the swelling and you should be fine.
One of my dogs was intent to eat bees,when she was a pup..in the end we took out all flowering plants in the dog areas,until she developed more good sense. I hope your pup is ok...if in doubt ,I would take it to the vet to get an antihistamine injection.
Re your wasps ...you could put up an old fashioned beer in a bottle trap for the lingerers.

> I did ask about anti hysts as I have them for myself, but the vet nurse said not to and allow the pups own immune system to deal with the sting

Not advice I'd be happy with.  There's no reason not to give Piriton but as WestCoast has mentioned you should check dosage with a vet if your pup has never had it before

I think I will talk to the vet next time I see him.

She seems ok, eaten lunch and is trotting about. Don't think a lot of the venom went in as I found the stinger bit in the middle of the iPad! Managed to quickly flip the wasp out of her mouth and stand on it, as she came rushing to me as soon as the wasp stung her. The only reaction I'm seeing other then some localised swelling, is that she keeps going out to wee, only a little at a time, but it is every few minutes. I wonder if this is the bodies way of clearing the poison from the system. She's also had two very tiny runny poo's which could be some sort of shock reaction.

Sorry only just seen this. When my male westie was a pup (8 weeks old) I saw him bat something on my slabs with his paw. When I went out to investigate, it was a wasp and by then my pup was sitting with his sore paw in the air. I phoned the vet and they said gave Piriton (they told me the dose that was suitable). I now carry Piriton on every dog walk just in case.

>there's no reason not to give piriton

Just in case anyone reads this thread historically and doesn't realise DogsaBabe knows this particular dogs medical history ( puppy in this instance) it is important to remember that there are some instances in which veterinary advise would be to not use Piriton.
This link (excerpt from The British Veterinary Association's Manual explains contraindications and indeed efficiency)
Veterinary Formulary- Antihistamines UK

For non emergency symptoms I've always found a dilute of vinegar to be brilliant for alleviating wasp stings... The old adage is B for Bees = bicarbonate of soda and V for Vasps = vinegar ( alkaline and acid)

Hope this helps :-)

> to stop the swelling as it's on the mouth

Especially if the sting is inside the mouth, particularly where any swelling could prevent breathing - not just in dogs and other pets, children as well. My son (when a toddler) picked up an empty fruit juice carton and drank from it, it contained a wasp which stung inside his mouth - fortunately the swelling was nearer the front of the mouth. I gave him ice cubes to suck (a dog might like these) which also helped :) Any fear that the throat/back of the mouth is affected, a trip to the vet/hospital may be necessary.

It's important to get the sting out, if on/in mouth or throat then I would go to Vet immediately. Too many in my breed have died from bee/wasp stings to the mouth/throat.