Question [Q] Not able to pick up a 4G LTE signal on my i9305...

Hi, I have a Samsung Galaxy S3 I9305 LTE which is originally from Three UK, but I have tried a couple of stock roms, one of which was unbranded from Germany and another one which is the EE UK one, all of these on Android 4.3.

Now my phone is able to pick up a 2G or 3G signal (be it 3G/H/H+ whatever) but it will not pick up a 4G LTE signal even though the same EE4G sim card I have will work perfectly fine with signal in my Samsung Galaxy Tab 3 LTE?

What am i doing wrong or is there any way to enable the phone to actually use 4G? (I have made sure the network mode is set to include 4G as "Auto Mode")

~ Many thanks for anyone who is able to offer me the time to help ~