Typically 3 months for a like for like job, but most firms can get round this by changing the reporting line for the new job or changing the job description in some way that can be called fundamental.
If you feel this is likely to happen for your own role then there is a good chance the company are using redundancy to get rid of you as an employee. You could fight it, but better to move on and start afresh.
Sorry to hear bout your reduancy ive also been made redundant the firm i used to work for is moving the factory abroad. Have you tried the citizens advice.