Most listings are in the $20's per square foot per year. The Heathrow region is going through a an increase in rates. In the last 3 months, the median rate increased $29 per sqft per year.
In the last 90 days, 3 listings have come on the market, which means leases are probably going fast. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,600 sqft. Most properties in this market are approximately 3 stories. Most buildings in this market were built in 1997 and are Class A.