My dad is adamant that I go into FY2 even though I can go into FY1

Have you worked in the UK NHS before? Many doctors I have worked with that have qualified abroad have not been able to work at the grade they were used to being in their home country as there is such a different in culture and systems, most had to step down to a grade below for at least 3 months, often 6 months before they were able to take on a similar responsibility level.

Remember as an F2 doctor you would be responsible for supervising more junior doctors who are newly qualified also and will need a high level of support to begin with.
The approval of your dad would be little consolation if you were to start your first job and find yourself underprepared.

However, compared to UK medical students, I've learned so little so far in my final year...

My dad says that there's not much difference in responsibility between FY1 and FY2 but is this really true?

...where I go straight into FY2 is not a wise move, no? Or does it really not make a big difference at the end of the day?

I've come across a handful of EU grads who have gone straight to FY2 and they have coped just fine. Statistically though, the drop down/drop out rate for this group is a fair amount higher than UK grads.

There was a case I remember on the first season of 'Help me I'm a junior doctor' - an Italian graduate became an FY2 in A&E. Well it emerged he'd never seen or heard of a neurological exam (its very common to just do a head scan in Europe), so obviously he couldn't continue and became an FY1 instead plus some additional training (note this might not always be possible but it was here).

Personally I would be wanting to skip FY1 if I could - there will definitely be a difficult adjustment and I'd definitely be writing off a month or so to bad times and long hours. But personally I do think if you make it clear to your supervisor and your seniors that just initially you are getting used to things and will need to call more often than normal, but also show a willingness to learn, then you'll get similar support to what an FY1 would get and you'll learn quickly.

Again to emphasise: FY1 is not really about learning medical knowledge. Most of your time is spent scribing for seniors, taking bloods and doing administrative jobs. Some users will disagree but personally I definitely forgot far more than I learned. Plus there is an applicability issue - ok maybe you'll learn something on your paeds/psych/respiratory medicine jobs in FY1, but how much does that help you when you start trauma and orthopedics as an FY2? Those were my actual jobs, in order!

What FY1 definitely will teach you though, is about NHS bureaucracy, working efficiently, time management, and communicating well with seniors. All important skills.

I'd personally go into FY2 but its entirely up to you.

Edit: also bear in mind the cost to you of doing FY1 - it depends on circumstance exactly how much you'd lose but because you get paid less every year from then on its certainly >£20k over the subsequent 10 years. Having to drop out though will of course cost even more.

What do you mean when you say "you get paid less every year from then on"?

Well you get paid less in FY1 than FY2. Then in your second year when you're earning FY2 wages you could have been earning ST1 wages, which are higher still. Etc etc.

So you don't lose £20k straight away - the FY1 vs FY2 difference is only about £5k so you'll only have to 'pay' £5k to do FY1 (versus FY2). But over time the cumulative pay gap widens and at a guess you'd lose £20k in the first 10 years.

The pay progression points only happen at FY1/FY2/ST1/ST3/Consultant. And so an ST7 will earn the same as an ST3 - hence it doesn't affect you for every single consecutive year. However you do still lose £20,000 overall as you say - £4,300 F1->F2, £5,700 F2-->ST1 and £10,000 for ST2->ST3. So you are right with the maths

Somebody thought it would be a good idea* to pay an ST7 the same as an ST3.
*Correction - a good money saving exercise.

Despite specifically mentioning the first 10 years, I think for some reason I had long term/consultant pay in my mind when I wrote that, which does still increase fairly gradually year on year. But yes you are right. In fact, your observation changes the dynamic a bit to mean that actually you can expect to lose £20k in the first 5 years before it flattens out/becomes too distant to think about, rather than 10. That's quite a substantial loss for a young person - that could be most of a houe deposit right there...

£20,000 gross taken from the top end of your pay over a number of years can only be interpreted after deductions. £20,000 - 9.3% (NHS Pension Scheme contribution) - 12% (national insurance) - (40% marginal rate of income tax) = £9,577. Less than £10,000 spread over a number of years isn't worth struggling at work or risking your long-term reputation by starting out as a sub-standard SHO.

Is £10k take-home worth struggling at work for a short period? Can I say... probably yes? There is an increased risk but its also the job you are qualified to do. Show me a doctor who wasn't nervous about starting FY1. You can't advise everyone to drop down a grade.

I wouldn't advise everyone to drop a grade but I'd seriously consider this if I were moving to work in a different country. It's not just struggling for a short period either. Reputations are important and no-one wants to be the "struggling" junior if that can be helped.

A lot depends on whether the OP has done a full year as a doctor or whether his/her sixth year was actually spent as a medical student. My understanding is that graduates of six-year medical degrees in European countries are considered eligible for full GMC registration even though they have not yet practiced medicine.