Depending on what you mean by older properties….
If you simply mean Victoria, with slate roof. Most Insurers will still accept this within their underwriting criteria.
Postoffice is a good recommendation I can offer, not a big name in the insurance market, but decent service, good prices and getting bigger by the day.
M&S seem to consistently get good press, albeit heard there prices have recently seen a big hike.
Halifax/Lloyds TSB Insurance remain good middle of the market people, reasonable service, decent prices.
Avoid the direct writers, Direct Line, Churchill,etc tend to be hard work if you ever need to claim.
If your in something Grade II listed, 15th century, or earlier, etc. then your choices will be quite greatly limited.
Brokers maybe a good bet for finding something half sensibly priced.
have heard good things about NFU, hear they are cheap, however no first hand experience.
I work in the insurance industry, hope this helps.