You're correct. You need a specific policy to allow for tenants renting your property. Allianz, Benchmark & Dolmen are all competitive for this type of cover. Do an online search or talk to a good broker.
I used an online landlord insurance company called Simple Landlord Insurance. Unfortunately we had to make a claim when the property was damaged by my tenants (bless) and my insurance company dealt with it very swiftly and in a professional manner. Hope this helps and good luck!
Just noticed that you have three posts since joining Askaboutmoney.com and all three recommend this insurance company. Have you any connection with the company?
allianz are very good - but I find each year when the renewal arrives it has nearly doubled in price. Always have to go online, get a new quote and then ring and try and battle them down to the online price.
We have our investment properties with 123.ie. Fortunately, we have never had a claim. I ususally ring them up when I get my first reminder and haggle over all properties and get a great quote. Very nice people to deal with. No affiliation.