Porto -
That sounds like a good system. I wonder why it needs to be linked to the tax system at all?
I think part of the reason the tax idea might not fly in the uk is it would be seen as an Upstairs-Downstairs thing - giving most benefit to high rate tax payers, less to regular tax payers and least to non-tax payers.
What about a system where each individual is allowed to purchase up to a standard number of cheques for £5, which can be used to pay for £10 worth of service? Everyone gets the same number, people on low incomes might be able to buy them for £2, say. People with high needs could be given more cheques either one-off e.g. When a baby is born, or on a regular basis e.g. for SN.
If you dont need any help, want to be a SAHP etc.. without extra help you could sell your cheques on an exchange and keep the money yourself.
Would create jobs, put more power in individual's hands, reduce bureaucracy?