Marriage confers "little if any benefit" in terms of a child's development, according to new research, challenging the rationale behind the prime minister's desire to offer tax breaks to couples who tie the knot.

New research by the Institute for Fiscal Studies (IFS) has found "little or no evidence" that marriage itself has any effect on children's "social or cognitive" development. Before the election the Tories had made the breakdown of the traditional nuclear family a key plank of their "broken Britain" analysis.