Property transactions are generally exempt from VAT, which means the associated input tax cannot be recovered.
It is not compulsory to register for VAT if ALL of your supplies are exempt from VAT or your taxable supplies are below the £81,000 threshold. If you have non-residential properties within your portfolio or other supplies that are not exempt you may wish to consider voluntary registration. This may also mean opting some or all of your non-residential land/property to tax.
Although this will then mean charging VAT on any taxable activities, you will also be able to reclaim the VAT on expenses relating to these activities. As long as your input tax exceeds your output tax in a given period, you will be able to reclaim the difference from HMRC. Dependant on the amounts of VAT you can reclaim you may wish to submit returns on a monthly basis. This would result in an increase in paperwork but allows you to reclaim monies back sooner.