Businesses, overseas governments and lobby groups have given sponsorship, free gifts and funding worth at least £1.8m to MPs and Lords in the past year through all-party parliamentary groups, Guardian research has revealed.

More than 300 all-party groups – semi-official groupings of MPs and Lords interested in a particular subject – have received funding or support from outside groups, including:

• Trips to 27 countries including China, Morocco, Azerbaijan, Taiwan, Thailand, Israel and Liechtenstein for members of 15 groups.

• A £32,000 donation from BT Global Services to fund concerts for the parliamentary choir.

• Contributions totalling more than £117,000 for "associate membership" – at £8,400 a time – of the all-party group on health, from companies including AstraZeneca, GlaxoSmithKline and actuaries Milliman.

• Free membership for MPs and Lords of the Slimming World all-party parliamentary group and the Weight Watchers group. Each group has about 20 members who are MPs or peers, drawn from all the main parties.

The data, which was compiled from an official register using a web scraper built for ScraperWiki, showed that contributions for which a cash value was given were up more than £200,000 on the previous year, which was the first time the Guardian analysed this data, and 60 more groups received some form of sponsorship or donations.

More than 80 groups issued parliamentary passes to staff with outside interests, which included several lobbying or consultancy firms, thinktanks, the Catholic aid agency Cafod and the Unite union.

All-party groups are obliged to provide some information on their donations, but when these are benefits in kind – such as free trips, dinners and administrative services – are not obliged to give their value. Despite being able to use parliamentary facilities and being regulated by House authorities, the groups are not made to publish minutes, information on whom they meet or detailed annual accounts.

Transparency campaigners said the groups' funding left them open to allegations of underhand dealings.

"The public has a fear that politicians are unduly influenced by people with money, and they need to work to tackle this perception," said freedom of information activist Heather Brooke, who was behind the disclosure of MPs' expenses. "Currently, because of the opacity of funding, these groups create the perception of lobbying through the back door. If they want to be seen as a respectable part of parliament, they should disclose more information on their activities and funding. If they aren't willing to do this, we really have to wonder why – what have they got to hide?"

Several lobbying groups are listed as funding the secretariats of all-party groups, but they are not required to disclose which of their clients – if any – provide them the finance to do so.

Contributions from outside groups vary from relatively small donations such as wine for tasting sessions of the all-party parliamentary wine and spirit group, or sponsored rugby kits for the all-party parliamentary rugby union football club group, to £16,000 for the parliamentary boat race from Siemens, to money to fund inquiries or reports on technology, health and abortion.

Overseas governments and interest groups are also contributors. Parliamentarians accepted a free five-day trip to Azerbaijan from the European Azerbaijan Society, which exists for the "promotion of Azerbaijan as a modern, progressive country with tremendous economic opportunities and a strong cultural heritage".

Members of the all-party China group received a trip to Hong Kong paid for by the Hong Kong government, trips to China supported by Virgin Airways which provided free upgrades, and accommodation from the Confucius Institute's headquarters and other bodies.

The speakers of both houses of parliament, John Bercow and Lady D'Souza, have appointed a working group on the conduct of all-party groups, looking into, among other things, "whether APPGs [all-party parliamentary groups] should be required to publish minutes and accounts; and the funding of APPG activities".

A spokesman for Bercow did not want to comment before publication of the working group's report, expected later this month. The group did not engage in a formal consultation but did take views from pressure group Spinwatch.

"There are a number of ways to funnel money into all-party groups, none of which are particularly clear," said Professor David Miller of the University of Bath, a director of Spinwatch. "Associate memberships, companies banding together to fund groups, and lobbying companies supplying services with no clear ultimate client are all issues. All-party groups perform some useful functions but these have been undermined by lobbying money."

Miller also warned that regulations covering "associate" groups, unofficial groups similar to APPGs which are not bound by even the restrictions on all-party groups, must be tightened.

Francis Ingham, chief executive of the Public Relations Consultants Association trade body, defended the role of all-party groups but echoed Spinwatch's calls for clarification on unregulated groups.

"The [association] considers APPGs to be a valuable vehicle for parliamentarians, including ministers, to interact with relevant stakeholders and the wider public," he said. "In the vast majority of instances the [association] considers APPGs to be effective and transparent. APPGs provide a vital role ensuring that government connects with specific issues, informing legislation and helping effective government.

"However, their effectiveness risks being undermined unless the distinction between APPGs and associate parliamentary groups is strengthened."

Read the full lobbying data at theguardian.com/data