I would say that you are quite possibly breaking law the twice.
The rules are quite clear around driving licences and in your case you have done the correct thing by applying for a GB driving licence.
Although your Omani driving licence may still be valid; according to the DVLA it is no longer a valid licence to drive in the UK as you have been a resident for over 12 months. This means that if you would not be able to use it to hire a car.
You also cannot hire a car using your GB issued licence as you need to have held it for a minimum of 12 months.
If you were to hire a car using either of these licences you'd be breaking the law as you'd be driving without a valid licence.
As you do not have a valid drivers licence to hire a car with, you would be breaking the law again as your insurance would not be valid; and you'd be driving without proper insurance.
I'm afraid you will have to wait 11 months to hire a car. Your options are to
- purchase a car along with MOT and proper insurance using your GB issued licence
- borrow a car from a friend as and when you need, ensuring that you are placed on their insurance as a named driver (their premiums will increase as a result of this)