Once the death benefit is sitting in the discretionary trust, depending on its value there may be a small IHT charge 1) whenever a lump sum payment is made out of the trust; and 2) every ten years on the anniversary of the date you joined the IBM pension scheme. In either case, the IHT charge would not exceed 6% of the value of the assets in the trust, and in many cases it would be substantially less.
If a 10-year anniversary falls within two years of your death, there will be no charge for that anniversary. Therefore, the first 10-year anniversary on which an IHT liability may arise is the first 10-year anniversary falling after the end of the two years from your death. The trust will benefit from a nil rate band (currently £325,000) which means that there is no IHT payable on assets up to this amount, although this can depend on your circumstances. The maximum charge at the 10-year interval will be 6% of the value of the trust assets above the available nil rate band.
The trust has its own limited annual allowance (£5,500) for Capital Gains Tax and gains would be taxed at 28% above the allowance.
Any investments that generate income would be charged to Income Tax at 45% (based on current rates) but if beneficiaries receive income from the trust, they can recover most if not all of the tax paid by the trust on the income they receive, if they pay Income Tax at a lower rate.