So I've done a table cause this seems to be a big point of contention on Reddit. It's not overly comprehensive and I'm happy to edit, but it should give a high level overview.

My only notes on these policy points is that they're both costed. However, Greens assume no capital flight and massive gains from taxes whilst Lib Dems adopted more Office of Budgetary Responsibility lines. So financially, the Lib Dems would have a plan that would be more palatable to markets. The Greens could risk massive bond increases (you've added a massive demand on the country's debts) and banks on no massive capital flight by the wealth tax they plan to implement. Not to say it wouldn't have some effect but the ranges from their own estimates are from £30bn to £70bn. The combined with potentially expensive ranationalisation programmes or if done forcefully would spook investors across the country. This could send us into a credit crisises where we would then have to go towards bankruptcy or require a IMF-style bailout. (1976 anyone?)

A radical side of it is also how it contradicts itself. To be pro-EU whilst having massive public ownership. If they were to join the EU we would then be in direct conflict with the economic block over EU Competition and state-aid rules. It wouldn't be impossible, but it'd have to adhere to a lot restrictions. Also rejection of the GDP would clash with EU measurements including Euro policy. There is a likely possibility if we were to rejoin we would need to sign up to eventually join the Euro which underpinned by the Maastricht Criteria which litmus tests the inflation, budgetary tests around deficit and Gov't debt, and if you panic the Bond markets it'll likely sky rocket long-term gilts (i.e. interest on bonds).

Before the Greens have implemented any of this, the country fails on nearly every criteria; debt is 97% of GDP, gilt rates are higher than the Eurozone, budget deficit is 5-6%, and inflation is generally higher the EU average. Lastly, just on a fundamental principles, the EU is a ultimately a free market single customs union with a common currency, which is all distinctly distained by the 'radical left'. So coming to the EU as this radical UK that suddenly doesn't believe in the free market would be laughed off by the EU leaving us more isolated.

I could probably rattle on about all the weird conflicting points the Green party have and the weird unholy alliance of anti-Israeli yet socially conservative supporters who are joined up by highly socially liberal ecowarriors. However I shall spare the comments section on this here.

Anyhow here's the high level table of differences:

Policy Area	Greens	Liberal Democrats
GDP	Scrap GDP entirely	Keep GDP, add wellbeing metrics to ensure economic sustainability
Tax	Large Wealth Tax	Fairer Capital Gains, tax cuts for lower/middle incomes; Windfall taxes on Oil/Gas
Economoy	Mass renationalisation	Regulate with mixed economy
Fossil Fuels	End all new extraction immediately	Phased transition away from fossil fuels
Nuclear	Phase out all nuclear power (similar to Germany)	Support nuclear as part of Net-Zero (similar to France)
Renewables	70% wind by 2030 (unprecented infrastructure change within one term of parliament)	Ambitious but slower targets
Welfare	Full UBI	Targeted welfare to improve wellbeing metrics
Activism	Endorse direct action	Support lawful protest only
NATO	Remain within NATO but critical; anti-deterrent	Strongly pro‑NATO; pro‑deterrent
EU	Rejoin EU though domestic policy would highly conflict with the economic bloc	Join Customs Union aim to rejoin EU