I'm a piano teacher and I agree with Natasha.
Yes, it's true that "there's no replacement for a real piano", IF and only if you have the budget from a properly decent real piano, and that means a minimum of 2-3K new, or having the knowledge, luck or contacts to be able to tell what is good second hand (and probably still spend about a grand).
The thing that is often overlooked by people pushing the real piano route is tuning. If you buy an old banger for next to nothing, it may not only be out of tune (which doesn't matter), but be incapable of getting into tune or of holding its tuning (which does!). This is terrible for the ears and enjoyment of those learning on it. OTOH, an electronic piano around the £500 mark wil be perfectly in tune and stay that way with no trouble whatsoever, while also having an action close enough to a real piano that it will make no appreciable difference to someone in the early years of learning. You could even get one cheaper than that second hand, and whatever problems it may have (probably just cosmetic), tuning won't be one of them. It'll either switch on and play, or it won't.
Learning to play music is about training the ear as much as training the fingers. The first is at least as important as the second in the early years, and can't be done properly with a piano that sounds like a metalworking factory.
Just get something with a proper weighted action. Yamaha P series (not sure what number they're up to now) or similar are good. Korg SP250 - slightly less natural sound than the Yamahas but decent action. Avoid being taken in by loads of bells and whistles - lots of different sounds, auto-accompaniment features etc. These will only be distracting, and mean that the investment into the instrument for its price point has been into those rather than the important things: piano sound and action.