Post back if something happens.
At the moment we'd just be guessing as to what the ex-employer is likely to do.
The ex-employer is unlikely to get an order without a hearing to which you get notified. It can happen in rare circumstances for the protection of trade secrets and intellectual property.
I'm sorry but this is just not accurate. In fact it is quite the opposite and is typically how an injunction (interlocutory in this case) would begin. An
urgent application is brought before the court, without the other party being present, it's purpose being to maintain the status quo - Somewhat unusual you might think but it's origins are in equity rather than law.
This is also the case with freezing orders so forth etc. Unlike specific performance, courts may order injunctions to compel or restrict behaviour to restrain breaches of equitable obligations or assist in enforcing legal obligations.
To the Original Poster: What sort of job are we talking about here?
Is there a restraint of trade clause in your old employment contract? (This is key)
At common law, the general rule is that restraint of trade clauses are void and remain contrary to public policy unless the restriction in itself is reasonable. In answer to your question. If your ex-employer were to commence proceedings against you, you would receive notification of this. However, (without going too far into it) there is a chance your new employer may also receive notification.
I imagine that the ex-employer would seek an injunction (provided there are grounds for it). Possible that you could seek declaratory relief, if you wanted to.. Of course, it's all dependent on the particulars of the case.
If you're worried, you should seek legal advice.