VAT on short term rent
VAT on rent is a deeply complex issue, so PLEASE don't rely on this post, but go and get professional advice. However, the following may be helpful:
1. It sounds like you own your premises. Do you?
2. When you bought your premises, did you have an entitlement to reclaim the V.A.T. on the cost? i.e. was your premises built since 1972 and always used by a vat-able business, thereby remaining in the vat net?
3. If both above are true, then doing a short term lease now is regarded as a "self supply" - i.e. taking the property out of the VAT net, but triggering a charge now (i.e. a VAT liability for you). I am not sure what the rules are for a partial self-supply, where (as in your case) you let out a part only of the property
4. If this self supply VAT charge is indeed your scenario, you can avoid this VAT charge by opting to account for VAT on short term rents (for VAT purposes short term is up to 10 years) BUT if you have other non-vatable rental income (i.e. a house) this option is not much help.
In short, you really, really must take professional advice. Sorry to be such a doom-monger