From Wolf's link:
Who can get Jobseeker's Allowance?
To get Jobseeker's Allowance you must be:
•available for, capable of and actively seeking work
•aged 18 or over but below State Pension age
•working less than 16 hours per week on average, depending on the amount of your wage
•in Great Britain
So once working 16 hrs p.w. you are no longer elligible to claim Jobseeker's Allowance. However, you can claim Tax Credits (from the same website):
Tax credits
A tax credit is a payment that you receive regularly. Despite the name, it isn't a credit against your tax bill.
Nine out of ten families with children qualify for tax credits, but you don't need to have children to claim. You may also qualify if you are working and on a low income.
Tax credits may also be able to help with the costs of your childcare. Generally, to qualify for help with childcare costs through tax credits, you'll need to:
•work for at least 16 hours per week
•have worked more than 16 hours per week before going on adoption, maternity, paternity or sick leave