A contract can be for any duration that the parties agree to. In my experience it is not unusual to agree on a rolling 6 month contract. That is, it keeps gett

A contract can be for any duration that the parties agree to. In my experience it is not unusual to agree on a rolling 6 month contract. That is, it keeps getting renewed every 6 months for years if necessary. I have found this arrangement preferable to an up-front multi-year contract as it allows for unforeseen changes in circumstances and requirements. For top-level management roles 3-5 year contracts are common. You don't explain why you mention the London rate. Longer term contracts generally offer a lower rate due to the perceived increased annual income. But that is just another aspect to be negotiated.