Nick Clegg has taken on an agent to manage his after-dinner speaking engagements, but has distanced himself from a website which is offering his services for up to $55,000 per speech.

The former deputy prime minister and ex-leader of the Liberal Democrats is listed among the speakers on the website of events company Leading Authorities, which boasts that Clegg can speak five languages and “occupied the second highest office in the country at a time when the United Kingdom was recovering from a deep recession following the banking crisis of 2008”.

“I’m happy to announce that former UK deputy prime minister Nick Clegg is now working with Leading Authorities for speaking engagements,” reads a promotional email from the company, seen by the Guardian. “Freshly out of public office, he was at the heart of every major political decision of the coalition government.”

The MP for Sheffield Hallam resigned as Lib Dem leader the morning after the general election, when it emerged his party had lost 48 of its 56 MPs and two-thirds of its voters.

A spokesperson for Clegg said: “Like all former leaders, Nick Clegg gets lots of invitations to speak at various events and recently took on an agent to manage these invitations. However, he was not aware of, and did not authorise, being listed in this way on this site.”

A promotional biography on the website says that “despite the hugely controversial decisions needed to restore stability to the public finances, Nick Clegg successfully maintained his party’s support for a full five-year term of office”.

The website lists the charge for Clegg to speak in the UK and elsewhere in Europe as between $35,001 (£22,460) and $55,000 (£32,000) and asks interested parties to enquire about charges for speeches at events outside of Europe.

Clegg follows a long line of former heads of government to use their experience to earn extra money through speeches. In 2011, the former prime minister Gordon Brown was paid nearly £75,000 to give a speech to a conference organised by the non-profit ANAP Foundation, which promotes good governance in Nigeria.

In 2009, Brown’s predecessor, Tony Blair, made around £390,000 for two half-hour speeches delivered in the Philippines. William Hague, the former foreign secretary who left parliament at the last election, charges from £25,000 for speeches.

It comes as research from the campaign group Unlock Democracy shows there has been a slight increase in the number of MPs with second jobs, at 114, up from 108, according to a BBC analysis conducted in February 2015.

Of the MPs who won seats for the first time in 2015, 19% have a second job, compared with 17% of returning MPs, the report found.

According to the new register of MPs’ financial interests, the Conservative party has the highest number of MPs with second jobs, with 84 out of 330 MPs (25%). The SNP has the second-highest number, with 11 out of the party’s 56 MPs (19.6%) and the Labour party comes in third, with 18 out of its 232 MPs (7.75%).

A total of 18 MPs reported doing regular media work or speaking engagements and 27 reported having a paid directorship, consultancy or advisory role. Five reported advances for books they are currently writing. Nick Clegg has not yet declared any outside earnings.

The issue of MPs’ second jobs was thrown into the spotlight in March when journalists at the Daily Telegraph and Panorama secretly filmed former foreign secretaries Jack Straw and Malcolm Rifkind discussing ways they could use their positions as politicians to help a fictitious Chinese company in return for thousands of pounds.

A YouGov poll conducted earlier this year found that 54% of voters favoured a ban on second jobs for MPs, while only 26% agreed that MPs continuing to do second jobs like medicine, law or running a business keeps them in touch with ordinary people.