In the last 90 days, 2 listings have come on the market, which means leases most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 50% of the available leases in the London are subleases, so you might be able to find a shorter term or below market rent. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around sqft. Most properties in this market are close to 2 floors. Most buildings in this area were built in 1959 and are Class C.