Can you do an economics PhD after doing an international political economy masters?

Maybe in econ theory, but almost certainly not in applied or quant.

So the only way to do it without an undergrad would be via the GDE, then a masters

PhDs don't work like that. As a short hand, someone might say they have a PhD in Economics, but their research might have been on the economic impact of the Corn Laws on money flows between France and Great Britain as a model for model for international migration and money flows between Albania and the UK. That would need quite a different academic background to someone doing research into the impact of the removal of inheritance tax, for example. both might be PhDs studied in a Economics Department though.

A PhD is a very specific piece of research that you have to have the academic background to support. The academic background comes first, and then you define your research proposal, and then you find a Supervisor, and that's when the Dept arrives. Even then, you tend to flex how you describe your PhD to whomever you are talking to - mine can be described as Politics, Philosophy, IR, ethical policy-making, or any combo if those, or even it's actual title!

So if you had a philosophy undergrad, and did all the political modules, you might get a Pol Theory Masters offer, but you'd be hard pressed to do a PhD in an Economics Department unless you took a very specific set of pol theory modules and the right dissertation and your research proposal was based on all that and could be best supervised in Econ.

wait hang on:
So my one would look like this:
Philosophy
Politics
IPE

Would this not work for an Econ PhD?

Do you have an actual project in mind? Which falls within the economics department research areas? That you have the relevant background to undertake? That's what the PhD is after all.

bro this is ages away, im a first year…. If I were to do:
Philosophy
Political theory
IPE
Would this be a decent background to do a politics-focussed phd?

Well if you're first year why are you deciding to do a PhD in another subject after doing a masters in another subject?

Just do what you find interesting and enjoy in your current degree and see where you go with it.

Ok so here’s the thing:
I currently plan on doing law/ I go to a good top 10 uni, law pays very well, and is the “obvious” path for me because philosophy, history, politics are the degrees that most people convert to law from, and it kinda makes sense- these areas are all fine for law, very good. I’m doing well in my tests, I’ve joined the law society, non law into law society, have gone to a few events, and signed up for open days at law firms… before converting: the plan is to do a political theory masters (ideally at Oxford), because then I get to call myself an Oxford graduate, and do a subject I’m really interested in.

But:

The world is going to hell. Yeah great: in 30 years time I’m a lawyer living my best life with a family… but what is the point if the world is hellish:
The house I’ll never be able to afford is underwater
Art is dying due to ai
War is CONSTANTLY becoming more likely
And so basically: I wondered if there was a way to stop it- so looked at politics
If I succeed, then yay, apocalypse avoided: if I fail, nice life as a lawyer whilst the corporatocratic hellscape burns around me.

So the plan was
Philosophy
Political theory (gives me an added year to try and enter politics, maybe, ideally something like SpAd or a diplomat)
IPE (a beneficial course for anyone entering politics)
PhD econ (justifies action- looks credible, and also bolsters support by looking like I contributed to human knowledge)
MPP (fundamental understanding of lawmaking, and government)

And now: I am trying to figure out the best way to achieve all this (if possible)— it conveys a very good range of political ability, philosophy, international relations, economics, government, and politics, and shows a very clear progression from the theoretical to the applied

This is...convoluted.

Why not just do a law degree to start with?

Also you don't need any degrees beyond an undergraduate degree in any subject to go into law anyway in the UK. You could just do your philosophy degree then take the SQE then get a training contract (easier said than done but that is the basic route).

Like honestly all this is just...completely unnecessary. And I don't think you're even doing them for the right reasons.

Yeah the plan was law conversion

What do you mean?

OK, well no, your first plan 100% isn't possible and isn't going to happen.
You can't plan life like this. You are trying to plan your A levels while you are still in nappies, it's a complete waste of effort. You need to master potty training, ie get your UG degree before you start thinking about your mid-life crisis!

Hang on…
The law conversion isn’t possible
Or global saviour plan isn’t possible?

The undergrad in philosophy followed by Masters in political theory, followed by PhD "in economics"