This is the angle I'm coming from. Pouring more state money into the problem seems to be treating the symptoms in a very inefficient way (especially if it's also going into the bank accounts of people not struggling to pay), rather than dealing with the causes.
Next thing would be that right wingers would be complaining that taxes are too high and expenditure should be reduced. I really do not deserve a free handout of £100.
It's probably a lot cheaper to give £100 to everyone than to try to means test it.
Is it £100 for everybody or £100 per household.
Easy way to means test it is to "pay" it through HMRC. Challenge comes if it's per household (which is probably fairer) rathe rthen per person.
French have a very efficient system for such things eg different energy efficient measures qualify for different Government subsidies (even different phases of an energy efficiency project). I undertook one such. No applying, you just pay the contractor and get an invoice that includes the appropriate reference codes and submit that invoice with your tax return and the refund is applied to your tax bill and if that goes into credit they (quickly) pay you a refund.
eg Government decides it's going to give 50% subsidy on ground heat pumps. There is no limit to the national subsidy level ie not €100m and when it's goner no more claims, everybody for works that qualify gets the 50% through tax authorities.
Going through HRMC makes means testing a lot easier as they already have the income information to automate. If the mechanism is going to be used per household then maybe add an option to a tax return "Claiming household allowances for <address>" (and multiple people claiming on same address is fraud).