Yes, in most cases. The best option is to have the whole block insulated. This will give the block a consistent look.
Depending on your tenure (the type of ownership you have, or the type of lease you have) you may require permission to have the work carried out.
It may be possible to just insulate the wall outside your flat, but not all installers will offer this. If in doubt, it’s best to consult a few different installers.
A list of accredited installers can be found on the National Insulation Association’s website: National Insulation Association