It is illegal to offer, promise, give, request, agree, receive or accept bribes - an anti-bribery policy can help protect your business. You should have an anti-bribery policy if there is a risk that someone who works for you or on your behalf might be exposed to bribery.
See: UK Government Anti-bribery policy.
Take elementary precautions to learn about potential business partners. Graft and corruption are common in many countries. The line between what's customary and tolerable, and what's excessive or illegal, is not always clear. If necessary, seek advice from a lawyer or a country specialist in a trade assistance organisation.
N.B. The UK Bribery Act (“the Act”), which entered into force on 1 July 2011, has consolidated the existing law, and has introduced a new offence of failure to prevent bribery. The Act is very widely drafted, and has an ambitious territorial application, which extends far beyond the shores of the United Kingdom.