i am shocked you found 38 people prepared to work for guaranteed 6hrs a week on a flexiable basis
This is part of the problem, filtering through the applications.
It is likely that most will not be suitable and of the ones that are a couple will seem OK or perfect for the job. When you give them the job, the odds are that they will let you down.
Very negative comments, I know, but when offering just a few hours, even more so when the hours are not set, you find that the successful candidate is looking elsewhere for work. Let's be honest, who wouldn't. There is also the chance that they just can't be ar5ed to turn in.
One option is to line up a few possibles so that if one can't cover then you can call someone else.
The best option for this case scenario is use an agency. They will be able to supply as and when at a cost of around £8.25 per hour (+ VAT). The only downside is you'll have to agree a guaranteed minimum shift. You should manage 4 hours if you shop around. Due to the nature of this work I'd stick with the big boys as they're more likely to have available staff at short notice.