The Ministry of Defence has spent more than £200m on studies for a new generation of air-deployable armoured vehicles that may never leave the drawing board - far less the ground, MPs warned today.

The Commons Defence Committee said that while troops fighting in Iraq and Afghanistan were having to patrol in 40-year-old "retread" personnel carriers and inadequately protected Land Rovers, the promised fleet of lightweight vehicles might be "unachievable".

The Future Rapid Effects System (Fres) was supposed to deliver a family of up to 3000 armoured fighting vehicles weighing less than 18 tons each to allow them to be flown rapidly to troublespots.

Harsh experience of the vulnerability of road patrols to bombs and anti-tank missiles in Iraq forced the MoD to insist on more armour, increasing the basic weight to between 20 and 27 tons.

This makes the vehicles too heavy to be flown in most RAF aircraft and possibly even too heavy for the next generation of A400M transports due to come into service from 2011.

Plans for Fres were first drawn up in 1998, but nine years later the idea "remains nothing more tangible than a concept", according to the committee.

In the meantime, a number of expensive collaborative projects involving Germany and the US have been abandoned and the MoD has been forced to spend even more money buying stop-gap vehicles and converting Cold War-era carriers to mine-proof standards.

Trials of three prototype Fres candidates are due to be carried out this summer after a two-year, £120m development phase which is itself running late. The MoD admitted yesterday that the most optimistic in-service date if the vehicles could be produced had slipped "to the early part of the next decade".

The Defence Committee warned that spending £147m upgrading armour on existing vehicles and a further £120m buying 100 specialised Mastiff and Vector vehicles was little more than a stop-gap solution.

James Arbuthnot, committee chairman, said last night: "The MoD has still not decided what it wants, let alone placed contracts for delivery. Meanwhile, our soldiers in Iraq and Afghanistan are expected to make do with a mix of old vehicles and stop-gap purchases."