The UK Government has launched a "Fix Your Bike" voucher scheme for England residents. The voucher can be used by anyone who has an unused bicycle in need of a repair. There are two vouchers maximum allowed per household, but the Government asks people to "consider the needs of others" as there are a limited number available. The vouchers can only be used with bike mechanics or repairers who have signed up for the scheme; see this map on the Energy Saving Trust website for your nearest partipating bike shop.
More background and guidance on the gov.uk website (Fix your Bike Voucher Scheme: apply for a voucher)
To actually apply for a voucher, head over to the Energy Saving Trust Fix Your Bike Voucher Scheme - Application Portal. You should end up with a voucher that you can present to your bike shop. You may need to be patient though! The scheme is proving to be extremely popular, so check back regularly to see if you can apply for your own bike repair voucher.