I think you should tell the truth - you can quote a figure for your overall package which includes bonus, and that will be higher than the £50k salary, and you could also add on company pension contribution as part of your overall package, but I wouldn't lie about your basic salary - when you start, you'll need to submit a P45 and they would see then how much you earned: I'm not sure of the consequences, but would you want to risk it, when you could get the job on merit? If it's advertised at £80k, and you have the right skills and experience, it may be that your previous job was underpaid; your interim work experience significantly boosted your skills and capabilities and you earned the pay rise, or that the potential job is just incredibly well paid.