When the Labour peer Lord Taylor of Blackburn was forced to apologise last year for improperly asking a question in the House of Lords on behalf of a paying client, the Sunday Times Insight team decided to investigate further. Undercover reporters posing as lobbyists contacted 10 peers; five Labour, three Conservative, one Liberal Democrat and an Ulster Unionist, to seek help in amending legislation on behalf of a client.

The results reflect badly not only on the House of Lords but also on the Labour party. Of the 10, four were prepared to do business with our “lobbyists” for fees of up to £120,000 a year. All four were Labour and two were former ministers.

Lord Taylor boasted that he could pick up the telephone and arrange meetings with Lord Mandelson, the business secretary, and that he had succeeded in changing legislation on behalf of Experian, the credit reference company. Lord Truscott, a former energy minister, said he had helped to change the energy bill on behalf of a company selling so-called “smart” electricity meters.

All four Labour peers – the others were Lord Snape, a former Labour whip, and Lord Moonie, another former minister – offered to help secure legislative changes by putting in a word with ministers, civil servants, or with the relevant members of parliamentary committees. One boasted of the huge amount of such business done in the Lords.

Since this newspaper revealed that MPs could be bought by lobbyists during the “cash for questions” investigation more than a decade ago, the House of Commons has tightened its procedures. The committee on standards in public life was established under Lord Nolan and toughened the register of members’ interests. Nobody would pretend the Commons is perfect but the easy corruption that was possible in the past has become more difficult.

The House of Lords is different. The assumption has been that its members can be expected to behave like gentlemen. The Lords has always seen itself as above the fray, with standards of conduct superior to those of the grubby Commons. That, it appears, is far from the case – and this is not merely of academic interest. Its role in amending legislation is important, as is the ability of its members to influence old pals in government who are in the process of framing laws.

Baroness Royall of Blaisdon, Labour leader of the House of Lords, said in a statement yesterday: “I am deeply concerned about these allegations. I have spoken to the members who are the subject of them and I shall be pursuing these matters with the utmost vigour.”

She is right to be concerned. The Sunday Times has exposed an important loophole which has to be closed. Increasingly the House of Lords has been targeted by lobbyists because they were coming under too much scrutiny in the Commons. The only solution is to prevent peers taking money in exchange for amending legislation and to insist on them making all their other outside business practices transparent. It is the only way to end the stench of corruption.