Under certain circumstances, HMRC allows the cost of childcare vouchers to be deducted from gross earnings (so they are free of both NICs and income tax). Whether your husband is entitled depends on the detail of the scheme - the rules are in this leaflet.
http://www.hmrc.gov.uk/leaflets/ir115.pdf
However the easier way to work out whether he's been tipped into the 40% tax bracket is to take a look at the personal allowance coding he's been given by HMRC for this tax year (2013/14). If it says 944L, he has the full persoanl coding and he will just about scrape under the threshold - especially he is in a contributary pension scheme. If it is considerably less than 944 - say around 600, then he's being 'charged' for his childcare vouchers through a reduction in his tax code. This would seemingly throw him into the higher rate bracket.
It's not the end of the world, you know - some group's got to pay for all these social schemes and endless extra demands being fought for in places like the NHS. Ed Balls may keep whining on about millionaires benefitting, but there are precious few of them to fund the country - it's the millions of middle-income earners that really fund the country.