The compensator (usually an Insurer) has to be in receipt of a valid certificate to pay compensation - they do not have to be in receipt of a nil certificate specifically. That said if you are claiming for damages from which benefits reclaimed by the state can be offset then you may find the amount of compensation you receive will be reduced.
Only certain benefits can be offset against certain heads of damages. For example your compensation for general damages (the amount you receive to compensate you for your pain and suffering) is ring fenced and while by law the Insurer has to be in receipt of a valid certificate to pay this to you, they cannot make any deductions in relation to benefits repayable to the state against this amount. However if, for example, you were unable to work as a result of your injury and were claiming loss of earnings as part of your claim but were also claiming job seekers allowance within that time because you were not working then the state is entitled to reclaim the money from the Insurer as part of the claim from your injury and that will be offset against your claim for loss of earnings i.e. the amount you will receive will be reduced in accordance with the amount of benefits that are repaid. The reason for this is to ensure you are not double compensated (the law allows you to be put back in the position you were in financially prior to the incident but it does not allow you to benefit from the claim - you can only claim job seekers allowance because you were out of work - you would not have received that money had you been in work - therefore if you were paid the full amount you would have received in earnings in addition to the job seekers allowance you were paid by the state then you will have profited from the claim, which is not lawful. It is not a case of the Insurer "footing the bill" it is ensuring the state is compensated for money they paid out as a result of the defendants negligence and ensuring that the claimant is put back in the financial position but not profiting from the defendants negligence.
In the case of the person who was paid cancer (for which I am truely sorry) if the benefits were paid out for reasons that have nothing to do with the injury for which you are claiming (severe ill health being a prime example - the medical expert confirms the injury you suffered in the accident would not have prevented you from working or would not have resulted in any other form of benefits, although the Insurer would have to deduct the benefits from any relevant section of the claim in the first instance, they can lodge an appeal to CRU to challenge the certiicate on the basis the benefits claimed do not flow from the incident - if the appeal is successful then the relevant compensation can be repaid to you. You can also submit an appeal yourself if the Insurer will not (though they almost always will) however it has to be submitted within 1 month of the benefits being paid or the right to appeal is lost.
The other thing to remember is that if you are claiming for loss of earnings from 1st January 2011 until 6th June 2011 but you didnt start receiving benefits until 3rd March, then the repayable benefits can only be offset against the amount you have claimed in loss of earnings from 3rd March onwards; as you were not receiving benefits from January up until March then you are entitled to receive the full amount you lost within that time frame.
Finally if a benefits certiticate is received for benefits which are not relevant to the heads of damage you are claiming (for example you are receiving the care component of a Disablement Pension but you are not claiming for care as part of your claim, you are only claiming loss of earnings) then the amount claimed in benefits cannot be offset against your claim as it doesnt apply to any of the items you are claiming and the Insurer will simply have to pay this in addition to what they pay you (assuming they do not have a right of appeal against the certificate)