Personal allowance
If your income is on the borderline of £100k (when you start to lose personal allowances) consider if it would be better to take some holiday before 5 April rather than earn income that is taxed at 60%. When you take pension, tax, NIC and student loan repayments into account, you could take home less than a quarter of your gross fee.
Also, if you hit £100k you will lose your tax-free childcare. So that extra session could be very expensive.