Hi,
Article 20 of the tax treaty between the UK and India
UK/India Double Taxation Convention does not mention lump sums.
This means that HMRC can tax your lump sum. It also gives India the right to tax the lump sum.
You would need to claim a tax credit in India for any UK tax paid under article 24 for the elimination of double taxation.
If you take a regular pension payments paid at regular times, then this is only taxable in India.
Thank you.