The school fees point seems to make sense. Death duties since the 1930s ruined many a rich family as they were so high. I think higher than the current 40%. I suspect LL did not have that much left and to lose a large percentage in death duties would have meant they would be unable to pay school fees for the children. I am not sure everyone had bothered by the 70s to put family money into trusts. If it were in a trust LL would not have been gambling it away.
It might even have been 75% if were very wealthy (1975 rates):
"The UK introduced estate duty in 1894 as a tax on property passing on death. By the time estate duty was replaced by capital transfer tax, it had been extended to embrace gifts made by the deceased in the seven years before death. Estate duty was widely criticised as a voluntary tax – because it could be avoided by giving away property and living for seven years. Note though that no spouse exemption was introduced until 1972 and even then it was limited to £15,000.
Labour replaced estate duty with capital transfer tax in 1975 “to make the estate duty not a voluntary tax, but a compulsory tax as it was always intended to be.” CTT was based upon the fundamental premise that all gifts of property, whether made on death or earlier, should be cumulated together and progressive rates of tax applied to the ever-increasing cumulative total. It was intended as a cradle to the grave tax with
the passing of a taxpayer’s property on death being merely the final gift.
The reservation of benefit rules were not required because all lifetime gifts would be charged to CTT (although at lower rates). Importantly it extended the spouse exemption to cover all gifts between spouses without limit. The tax was highly progressive and the top rate of tax for cumulative transfers over £2m was 75%. "