The best companies offer genuine environmental and developmental benefits to the world, rather than a glorified holiday in the sun. People and Places works with local partners in Pakistan, Madagascar and South Africa (travel-peopleandplaces.co.uk), and Quest Overseas has worked on 14 projects across Africa and South America over the past 10 years (questoverseas.com). Both have policies for “responsible volunteering”.

Often the most worthwhile projects emerge when local people ask agencies to recruit volunteers. One of the most credible marine organisations is Blue Ventures, a not-for-profit organisation that has responded to a request from the Madagascan government to bring volunteers over to work on marine conservation projects alongside local scientists (blueventures.org).

The Ethical Volunteering website (ethicalvolunteering.org) has useful tips on choosing the right agency. I volunteered on an excellent 10-week expedition with the youth development organisation Raleigh International, which has long-established connections with local community groups and conservation organisations (raleigh.org.uk).

2 Way Development (2way.org.uk) and World Service Enquiry (wse.org.uk) provide long term placements, while Student Partnerships Worldwide offers students under the age of 28 opportunities to work with local charities in India, Nepal, South Africa, Tanzania and Uganda (www.spw.org).

· To ask questions or offer advice, go to greentraveller.co.uk.