Empty periods between lettings are expensive, writes Tony Booth.

They substantially attack annual yield and are a major cause of financial difficulty for buy-to-let investors.

Over the last few years, tenant fixed-term letting periods have gradually reduced.

The average is now just six months.

Although some tenants renew for a further six months - some don't - and this produces at least two periods every year when the landlord or their agent has to find new tenants for the property.