David Cameron is on his way to Australia to meet Commonwealth leaders as he reprised a foreign trip severely truncated by the eurozone crisis.
The Prime Minister will put efforts to change royal succession laws at the top of his agenda for the summit in Perth.
The bi-annual Commonwealth Heads of Government meeting is expected to agree historic changes to the 300-year-old rules to enable a first-born daughter to ascend the throne ahead of her brothers.
Mr Cameron is travelling to the meeting - the first since he became premier last year - directly from Brussels where he held emergency talks with fellow EU leaders on Wednesday in an effort to agree a solution to the economic crisis in Europe.
He was forced to scrap plans to visit both Japan and New Zealand en route after insisting - in the teeth of angry opposition from French president Nicolas Sarkozy - that all 27 EU nations should meet ahead of crunch talks among those using the single currency.
The gathering of leaders from the 54 countries that make up the Commonwealth is also likely to be marked by heated discussions about human rights after an internal report criticised the group's failure to speak out on abuses.
Among proposals from the report of the Eminent Persons Group to be debated is that homosexuality should be legalised in all member states where it is outlawed.
Lord Howell, the minister for the Commonwealth, said last week that he expected leaders of the 16 countries where the Queen reigns as monarch to agree to reform of the succession laws at the summit.
Mr Cameron disclosed earlier this month that he had written to the leaders of the countries concerned to canvass their views. Pressure for change has been building since the marriage of Prince William and Kate Middleton, with MPs calling for the issue to be resolved before any future royal children are born.
Previous moves to reform the 1701 Act of Settlement - which also bars Catholics from ascending the throne - have foundered on the need to change the law in all the countries concerned.