Former prime minister Tony Abbott has warned Malcolm Turnbull he will confront the same "no one can be worse off" mentality that bedevilled his government, as his successor considers a potential rise in the GST.

And he has also defended the polarising speech he gave in London last month, in which he promoted his government's hardline asylum seeker policies as a solution to Europe's migrant crisis, dismissing criticism as "carping from the usual suspects".

In an opinion piece for The Spectator, Mr Abbott suggests he backs the push for a GST increase – as long as it is coupled with other tax cuts.

"As a potential reformer, Malcolm Turnbull has the advantage of being relatively unbound by previous commitments but still faces the problem of how to deal with the 'no one can be worse off' mindset that makes serious reform so hard," Mr Abbott writes.