Conservative minister Ken Clarke has joined forces with Liberal Democrat Danny Alexander and Labour's Lord Mandelson to warn that leaving the EU would be an "historical error".
The politicians insisted the UK should work to reform the organisation from within rather than walking away.
Mr Clarke, regarded as the sole Conservative europhile in the Cabinet, said: "David Cameron has already shown what can be achieved in Europe through strong, determined leadership.
"We earn our living in a globalised economy and a world in which nations are interdependent in tackling global and regional problems.
"We can help to promote our own interests best by reinforcing our role as a leading nation in the EU."
More top news
Rain will slowly edge into Scotland, reaching Northern Ireland by Thursday afternoon. There will be plenty of cloud across the UK.
Clashes between rival supporters marred West Ham's EFL Cup fourth round win over Chelsea at the former Olympic Stadium
Jane Beedle, Andrew Smyth, and Candice Brown went head-to-head in a closely contested royal themed final.