I got to work today and the business where I work has signs outside saying premises "to let".
We have had no consultation or mention of closure or moving, our site manager does not know what is happening. Can the company do this ?
You've put this in Law.
Unless you find out from your employer more about the circumstances, it is impossible to judge whether the employer is in breach of employment law - but just for erecting a sign, no. It's the consequences you need more information about.