There are two main areas:
With the advent of the Insurance Act in August 2016 you need to fully appraise your insurance company of the risk.
They will want to fully understand how you will ensure that this is something that you can undertake and also where you see the exposures i.e. if your advice turns out to be incorrect what could the consequences be?
Even if your current policy coverage is worldwide geographical they may only note it within the UK and would see working in countries particularly outside of the EU as higher risk by virtue of differences in the law, language, penalties etc. Insurers are very nervous when North America is mentioned.
2 Terms and Conditions
It is really important that you have well drafted terms and conditions in place and they refer to the jurisdiction for contractual disputes as being in your home country.
It is also important that your client accepts your terms and conditions and you do not end up working under theirs. If this is the only way they will do business be prepared to walk away.