LONDON — Shares in newly-privatized Royal Mail soared on their stock market debut Friday, bolstering criticism that the company — which traces its five-century history back to King Henry VIII — was undervalued by the British government.
The shares rose 31 percent to $6.91 by midday, a hefty gain for shareholders who got them at $5.27. Nearly 150 million shares, or 15 percent of the total issue, changed hands.
‘‘One can only say that investors have clearly given their stamp of approval to the offering,’’ said Brenda Kelly, senior market strategist at IG.
But the opposition Labour Party argued the gains prove the government shortchanged taxpayers and could have gotten more than the $2.75 billion it received from the sale.
‘‘The government has a lot of explaining to do,’’ the Labour Party’s spokesman, Chuka Umunna, wrote on Twitter.
The privatization is symbolic for the Conservative Party, the main party in the coalition government.
Business Secretary Vince Cable, a member of the Liberal Democrats, the junior party in government, dismissed claims the sale had been undervalued, telling BBC Radio that the sharp price rise was no more than ‘‘froth and speculation.’’
Following Friday’s surge, the company is now valued at nearly $7.2 billion.