Central London investment turnover dropped by £2.2bn in the first half of the year, according to data from DTZ.
The agent said transactions were expected to end on £5.4m for the first six months to 30 June, compared with £7.6m in the same period in 2012.
The fall is the result of a lack of stock on the market. Availability stands at £1.6bn, around 25% below the £2bn available at the same time last year.
Overseas investors have continued to dominate purchasing activity, with 76% of all deals being undertaken by non-domestic buyers in the first half of 2013, marginally higher than the proportion in 2012, which stood at 72%.
In the first half the West End market saw the highest total sale volume with £2.1bn transacted, followed by £1.9bn of deals in the City. Some £700m of deals took place in the Midtown and Southwark markets.
Fergus Keane, head of West End investment, said: “The diverse and competitive nature of demand for West End assets has resulted in competitive bidding for the most attractive buildings, particularly where there are asset enhancement or repositioning opportunities.”
Martin Lay, head of City investment, added: “The market also remains highly liquid for large lot sizes, and we anticipate significant investor interest for Land Securities’ 2&3 Bankside , and Helical Bar’s 200 Aldersgate , both of which have just been offered for sale.”