Thanks for the well-wishes. It seems I was lucky and it was just a 24/48 hour bug, rather than the horrible Norovirus that's going around my younger dcs' school at the moment.
This afternoon I left Pip loose in the kitchen while I did a school run for the first time ever. I gave him a treat ball with his meal in, a large kong (plus a small kong for Lurcherboy) and a couple of busy buddies. Main reason for the extra treat toys was that Lurcherboy was so delighted to see his old treat ball and ran straight to it, so I was worried they may fight. I needn't have worried.
They scoffed their way through the lot, taking almost exactly an hour, which is longer than the green-feeder and kong combo he used to get in his crate. He then whinged a bit once he'd finished stuffing his face and I recognised it as his 'I need to go out Mum ' whinge, which would only get louder if I didn't respond, so let him out and he came back in and spent another ten minutes finishing off the last bits of kong. All in all I think it was a big success. Would have been better if the toys had lasted longer than an hour, but not bad at all. If I can just get him to the point that he stops eating and goes to sleep with a nice full tum I will finally be getting somewhere - and may even be able to go somewhere! 
I'm seriously thinking about buying one of the remote control cameras someone linked to on another thread. You can control it via your laptop or smartphone and it has two way audio, so you can speak to the dogs and give them the 'quiet' or 'settle' cue if they're making a noise. I reckon it's worth a try for a little over £30.00 and even if it doesn't help with the training, it will indulge my nosy side, that wants to know what they actually get up to while I'm out - rather than what it sounds like on a dictaphone recording. 