Its to do with how much you put into a pension rather than your personal income tax allowance.
The maximum personal contribution you can achieve tax relief on is 100% of your earnings. You are also subject to the annual pension contribution allowance which is £60,000. This includes all pension input, personal contributiuons to personal pensions and your NHS employer final salary scheme. Any contribution in excess of that is subject to an annual allowance charge.
With a personal contribution to a personal pension (i.e. SIPP/Stakeholder pension etc.) the contribution amount is straightforward - its the gross amount of money you put in. However, your NHS scheme is different, and is based on a notional input amount - how much your pension entitlement has increased by. Here is an example, sorry, its bloody complicated:
https://www.nhsbsa.nhs.uk/sites/default/files/2017-04/Annual%20Allowance%20Example%20calculations%20Factsheet%20v3.0%2010.13%20-%20Copy.pdf
Also, individuals with total income and employer contributions over £260,000 may have a reduced AA, potentially as low as £10,000 - different figures applied in earlier years. This is commonly known as the 'tapered annual allowance'.
So a £30,000 contribution may be the right thing for you, but it may also see you fall foul of the complex annual allowance and tapered annual allowance rule, and your contribution may exceed 100% of your earnings and not achieve tax relief.
So, sorry to derail your thread about selecting a provider for your pension, but your first consideration needs to be what you can contribute to mitigate your tax liability but ensure that you don't exceed the annual allowance and/or 100% of your earnings as this will render the exercise as pointless and may even leave you worse off. Once you've established that, you can start thinking about pension providers and funds etc.
I would caution against the DIY approach for such tax planning, and suggest that with cashflow planning, tax planning and investment risk considerations your retirement and financial wellbeing would be better served by employing a financial adviser (not SJP).