I agree 100% with Tony's comments - realistically, they're not going to quibble and the worst case scenario is you burn bridges with that particular firm.However, this whole topic has got me thinking. Does the fact that no rational firm will make somebody work for them if the candidate wants to reject the place prior to starting yet after having signed a contract mean that, if you have an offer from one firm but are maybe 2-3 weeks away from potentially receiving one from a better firm, you should sign up in order to 'bank' the offer and then 'gazump' them if something better comes along? My thinking here is that some firms might not take things too well if you ask them for a 3 week extension on their signing deadline because you have a few more interesting prospects in the pipeline (it kinda contradicts what you have to say in the interviews about always ever wanting to have worked for XYZ Ltd because they are the best thing since sliced bread), so rather than risk a sure thing, you reserve your 'seat' with that firm whilst the offer's there and then gazump them if necessary?