Hi Weedster and welcome to the forum!
Have you completed on your purchase yet? As part of the process, your lawyers should check that, if the property wasn't built with the balconies enclosed, the vendors have done so with permission from the community of owners (if there is one) and with planning permission from the Town Hall. If not, you will become liable for the cost of doing so, along with up to 4 years back IBI (Council tax) from the Town Hall. Ask your lawyers the question and, if you haven't completed yet, I'd recommend making it a condition of purchase.
Kind regards,
Kim