Hi Guys - On my Dot offer it says "you WILL be required to work at various locations across the UK and overseas depending on client requirements".RE overseas.....do I have a choice here? If they ask me to go to Russia, for e.g., can I say "no"?Sorry for the naivety.Thanks in advance.

No, you have little to no choice - that's what you are being hired for.

Depending on your grade you can normally kindly reject opportunities to go far abroad for long periods that include weekends. At junior grades there are normally enough people who will jump at such a chance. Therefore minimal nuisance to people and minimal impact on your progression (assuming you remain chjaregable) However at more senior grades you'll p1ss people off and life might be difficult...