The delay is a little on the wrong side of reasonable if your solicitor received a loan cheque.
If, however, the new loan was issued by electronic fund transfer, I would be slower to criticise, without knowing more.
Some lenders - very annoyingly - send the money by electronic funds transfer but can't seem to be bothered sending any communication to the solicitor for several days afterward (or their communication consists only of a call to say 'we are issuing funds' and frankly this is not always enough as phone calls can easily miss being logged or filed, in a way that does not happen with a fax or letter). Plus, if there is a delay or hitch, the solicitor does not have the option of returning the uncashed loan cheque for re-issue. All in all, electronic transfer of funds has not necessarily made life easier or cheaper in connection with mortgages.