If the your last sim check has expired by more than 5 years then it is an initial all over again. Anytime before that it is a sim check.
Try not to let any type you have on your license, that you intend to use in the future, especially without experience on type, expire more than the 5 years. Doing an initial TR you will also have to do the required amount of landings in the a/c, again. This can be very expensive, if you are self sponsored.
You can check this by going to the UK CAA website - FCL - Lasors and IIRC section 4, somewhere there.