Some rough calculations, based upon you earning £400 per week in your old job and not starting your new job until the new tax year starts in April:
You'll have worked for about 26 weeks, earning about £10,400. During each of those weeks, the first £240 you earned was tax free. So you were taxed (at 20%) on £160 each week = £32 tax per week, making £832 tax in all.
Your 'earnings' for the year (i.e. including JSA) were £10,400 + about £1260 = £11,660, which is below the tax threshold for the year. (i.e. you shouldn't be paying any tax at all for the current financial year).
Using those figures, you'd be entitled to a refund of all of the tax that you'd paid (£832).
If your earnings were higher than that, your total 'earnings' would be above the personal tax allowance, meaning that you'd be entitled to some of the tax you'd paid back but not to all of it.