Sit down and work out what people are searching for and how they search. Then develop an information architecture based on
area/city/county/postcode and have it accessible also by keyword.

The UK is very lucky to have a precise postcode system and you should make the most of it to build the structure. Limit the keyword searching to obvious terms such as short lets, flats, houses etc. Rather than use an off the shelf solution, it might be worthwhile to develop a database backend that makes storing such information easy. (Each property would be categorised in terms of area, city, postcode, type, price, minimum lease period etc.)

The biggest mistake that a lot of people building directories make is in giving the user too many options. That causes a lot of confusion. The trick is to limit the number of options while at the same time making the site more searchable in human terms.

Regards...jmcc