The solicitor is not running a bank, their requirement is that you have the funds available to them in a timely manner. Depending on what type of account the solicitor uses for their holding account, they may accrue interest but it is unlikley that they would have the inclination to calculate and disperse that interest. As the money needs to be available quickly when the purchase closes, it is probably not in a high interest bearing account.
There is no harm in asking but unless you have agreed with your solicitor a rate of interest that they will give you while they are holding your funds, I do not think that you are entitled to it