Can an employer change the terms and conditions of transferred employees if a certain amount of time has passed since the TUPE transfer?

Whether or not an employer can change terms and conditions following a TUPE transfer depends on the reason for the change. Any attempt to vary the transferring employees' terms and conditions of employment, whenever it takes place, will be void where the sole or principal reason for the variation is the transfer itself, and it is not an economic, technical or organisational reason (an ETO reason) entailing changes in the workforce.

The amount of time that has passed since the transfer does not play a part, other than that it will be less likely that a variation of contract will be seen to be because of the transfer if it happens after some time has passed. The employer must be able to show that there is another reason for the change that is unrelated to the transfer, for example an organisational change in response to a change in customer demand.