Four major political parties in Australia?

There are thousands of political parties registered with the Electoral Commissions in Great Britain and Northern Ireland, many of them have only a handful of members and only stand in local elections. Below is a list of political parties represented in the House of Commons;-

Labour, Conservatives, Liberal Democrat, Scottish National Party, Plaid Cymru, SDLP, Democratic Unionist Party, Ulster Unionist Party, Respect, Kidderminster Health Concern.

As well as the above parties, the UK independence party and the Green Party sends MEP's to Brussels. Sinn Fein has MP's elected to Westminster, but as they refuse to swear allegiance to the Queen, they don't take their seats in the House of Commons, however Sinn Fein do send some MLA's to the NI Stormont assembly.