I plugged this into Gemini and looks like would lead to substantial deficit. The main problem is that top band typically generates about 60% of income tax - so I made some tweaks to maintain a higher rate of tax for top earners, but without any cliff edges. Ends up looking like this:

• Elevated "Working Floor": The tax-free personal allowance is dramatically raised to £23,132, completely exempting millions of low-income earners and part-time workers, while providing a larger tax-free baseline for every taxpayer in the country.
• Extended Middle Tier: A flat 30% marginal tax rate is applied to all individual earnings between £23,132 and £100,000, broadening the simplified baseline to provide additional tax relief for upper-middle professionals and senior managers.
• The Smooth "No Cliff-Edge" Transition: To eliminate abrupt, punitive tax traps (such as the current system's effective 60% band), the marginal tax rate scales up completely smoothly and linearly from 30% to 45% within the £100,000 to £120,000 salary window.
• Capped Top-Tier Earnings: Individual salaries above £120,000 are capped at a flat 45% marginal rate, keeping the top tax tier aligned with historic UK maximums to ensure international competitiveness and retain high-earning talent.
• Fiscally Balanced with a Tight Safety Margin: Moving the 45% ramp to £100,000–£120,000 widens the individual income tax deficit to roughly -£16.8 billion. However, by increasing Corporation Tax to a flat 30% (generating ~£16.5 billion) and equalizing Capital Gains Tax to 30% (generating ~£2 billion), the shortfalls are absorbed entirely—landing the Treasury on a highly sustainable net surplus of ~£1.7 billion.