"The only issue with the lifetime interest suggested above is it effectively traps your husband in the house for the rest of his life, unless you have enough assets for him to buy somewhere new outright with his half."
I would disagree with you here.
In most cases, a properly written will, will allow the surviving spouse to move home and for the trustees of the trust to invest in the new property on the same basis.
"However, if she left her current house she would only be entitled to half the value so cannot afford to move. This was an unintended consequence,..."
This sounds as though it was a poorly written will. A typical will might include something like this:
The Property Trustees may at any time or times during the Trust Period as to the whole or any part of the Trust Fund in which the Life Tenant has for the time being an interest in possession:
pay out of any proceeds of sale of this property or any substituted property (purchased as a result of this sub-clause) to purchase a freehold or leasehold property which will be held for the benefit of the Life Tenant on the same trusts to which this clause refers.
In other words, the Trustees can choose to use all or some of the trust fund to purchase a share of a new home for the surviving spouse. They could agree to purchase 50% of the new home, or all of it, or none of it. Or, indeed, any other percentage.
It may be in this particular case that the will was poorly written and did not include such a clause, or it may be that the Trustees misunderstand the will or it may be that the Trustees simply do not wish to invest in a new home for the widow (you will notice the use of the word "may" - so they are allowed to do that but not required to do it) and so, in that case, if the Trustees decline to invest in a new home then, yes, the surviving widow just has her 50% to rely on.
So, just suppose that the widow does sell up and uses her 50% to buy a new home. What happens to the money left in trust?
In that case, the "remaindermen" (the people who inherit after the widow dies) don't get the money - they have to wait until the widow actually dies before they can get their hands on the money.
Until then, any income from the trust goes to the widow. I really would suggest that the Trustees speak to a qualified advisor if that is the case.
Any capital growth is retained by the Trust, but any income (such as interest or dividends) is paid to the surviving parent.
For example, if you put £100k in a savings account. According to Moneysavingexpert, the top rates at the moment are around 4.2%. So £100k in a savings account could earn £4,200 per year in interest and that must all be paid to the surviving spouse.
That's great for them but not so great for the children.
Alternatively you could invest in things that go for capital growth and don't provide any dividends at all. Great for the children, not so great for the surviving spouse.
However, the Trustees are required to take the interests of both parties into account (unless the will says otherwise - it might say that the interests of the surviving spouse may be solely taken into account) when deciding what to invest in.
This would normally be done by selecting a mix of investments, some of which concentrate on capital growth (good for the children) and some which concentrate on providing income (good for the surviving spouse).
I really would recommend that the Trustees speak to a qualified advisor about this.
Then, when the surviving spouse finally passes away, the assets of the Trust can then be passed out according to the will.