DD had to get all legal documents together etc etc. It wasn't the full HIP but the minimised one the last government introduced and this government cancelled.
At the end of the day DD's sale was delayed because even though you can give a solicitor every bit of information they need on day 1, you cannot make them read it. If Estate Agents, Mortgage lenders and solicitors are lazy or slipshod, and too many of them are, then house purchases will continue to take ages.
At the time the minimised HIPS were introduced I did a quick paper and pen assessment of every house purchase/sale we had been involved in, also children, close family, and friends, about 40 transactions in all and there was only one occasion when the HIP, minimal or full would have done anything to reduce the long gap between offer and exchange.
Getting documents, searches, surveys done is the easy bit. Almost all the delays were related to process, mortgage forms being lost or delayed, solicitors leaving everything until the last minute, buyers gazumping, sellers being unwilling to agree dates for completion or going on holiday at critical moments. In one case a buyer in the chain died. HIPS cannot deal with these.