A boom in the number of auctioned block trades has helped close the gap between the average issue price of a chunk of stock and its previous trading close to the tightest levels since 2007.

Accelerated share sales - in which investment banks sell a block of stock for a client over a short time frame - are sold at a discount in order to attract investors and account for increase in the amount of stock on the market. Data provider Dealogic estimates that the average discount applied to block trades stands at just 3.4% globally so far in 2013.