Income Tax Computation: Transferable amount of Personal Allowance.

Example 11 (Modified): David and Victoria are married and in 2018/19 David had a trading income of £11,000* and Victoria received a salary of £30,500. CALCULATE THE INCOME TAX LIABILITIES OF DAVID AND VICTORIA ASSUMING AN ELECTION IS MADE TO TRANSFER THE TRANSFERRABLE AMOUNT OF DAVIDS PERSONAL ALLOWANCE TO VICTORIA. *(Note: £11,000 was £8,000 in the original example, the modification was done so that the transferer’s total income is less than the given Personal Allowance (PA) of (£11,850) in 2018/2019 but more than 90% of £11,850). In other words, I would like to know the tax computation is like when the unused PA is less than 10% of the given PA (£1,190)?