Mr Mallard left last night on the "work trip" to see contacts related to his education portfolio, which he openly admitted had been deliberately timed to coincide with the test match.
"This is not a holiday," he said.
He said he believed going to the rugby was "fair enough".
"I'm not pretending I haven't deliberately timed it, but it is a trip I would have done at some stage anyway."
Labour leader Phil Goff would not comment on Mr Mallard's trip last night, despite yesterday castigating Maori Party MP Hone Harawira for having "skived off" to Paris when he was meant to be on offical duties in Brussels.
Mr Harawira had nothing to say when asked about Mr Mallard's trip.
"No comment," said Mr Harawira.
"If there's one thing I've learnt in the last couple of days it is to say: `No comment'."
A spokesman for Mr Goff said Mr Mallard informed him of the trip on Tuesday - a day after Mr Goff told media he had told his MPs to act with restraint in the current climate.
Mr Mallard publicised the trip yesterday on Red Alert, the Labour blog.
As a long-serving MP, Mr Mallard is entitled to a 90% discount for the flights to London.
His partner, former world champion rower Brenda Lawson, is not accompanying him, so he will not be using the partner perk and he will stay with a friend while there.
Mr Mallard said he was not concerned about using the perk despite the economic climate in which most private individuals and companies were exercising restraint.
"You can't put good policy development on hold because you've got an economic problem."
Mr Mallard said he would be meeting "a new generation of education thinkers" and finding out how policies had worked in the United Kingdom.
He said it was different to Rodney Hide's use of the MP's travel perk, as "I'm not being a hypocrite".
Mr Mallard will be a guest of the (England) Rugby Union at Twickenham.
He is also the Opposition spokesman for the Rugby World Cup and said he might meet International Rugby Board representatives while at the game, although nothing had been arranged.
