THREE leading political parties have joined forces and presented a counter proposal to the administration on retirement protection. United Democrats Yeung Sum and Lau Chin-shek, the Liberal Party's Henry Tang Ying-yen and Meeting Point's Tik Chi-yuen yesterday met for 50 minutes to discuss their position on the Government's proposal of an old-age pension scheme. Speaking after the meeting, they said they had decided to press the Government to fully fund the scheme and that it should commence next financial year. A means test, based on the one that applied to Legal Aid, should be introduced, they said. They estimated that the scheme would cost $7.5 billion, only $4 billion more than the current expenses on old-age allowance. The legislators said they would put their latest proposal to Governor Chris Patten as soon as possible. The three parties stressed that they would continue to fight for a central provident fund. A government spokesman said the administration would only comment after receiving the proposal. Last week, the Government proposed setting up a pension scheme instead of a central provident fund or compulsory retirement scheme. The administration suggested the scheme to be funded by monthly contributions from employers and employees and every old person should get about $2,100. But it fell short of saying whether it would also contribute. Nor did it provide a timetable for the implementation, saying the details of the plan had yet to be worked by consultants. Mr Patten yesterday described a central provident fund as a ''rotten bargain'' for Hong Kong people.