There are too many unknowns in your questions to give definitive answers. For example, is this to be a standalone system just for vinyl or do you need something with multiple inputs? What size of room does it have to fill with sound? What other gear have you heard to compare against anything new? Is this a one-shot deal or just the first step down the road to a better system?
Of all the gear you'll own, the speakers will have the biggest influence on the character of the sound, but they can only work within the limits of the signal they receive: Garbage in = garbage out.
The turntable and its cartridge dictates the quality of the signal. Unless built into the speakers, any outboard amplifier influences how well the speakers can be driven in terms of volume, dynamics and scale.
If I was looking for the best sound quality in an entry-level system, then I would go for a separates system based on purist TT, Hi-fi amp, and bookshelf speakers; but I would be hard pushed to achieve what I would class as a worthwhile purchase for £400 new.
The system would consist of a Pro-ject or Rega turntable (£180-£250), an Onkyo A9010 amplifier (built-in phono pre-amp) @ £180, and a pair of Wharfedale Diamond 220 speakers (£99). You would need to budget for interconnect cables and speaker wire separately. This would give a very musically-satisfing system with enough bass to keep most people happy, and it would play well at both low and high volumes.
An alternative would be something based on active speakers, but I am unsure whether something in the £150-£200 range would have the resolution and the bass reproduction of the separates system, so matching that with a very good TT up to the max limit of the budget might be a waste.
AT-LP120 TT or the AT-LP5 + Edifier R1700 speakers would come in somewhere around £400. This would be the 'bells and whistles' system where you get facilities such as the USB output and infrared remote control. Sonically it wouldn't be as accomplished as the purist system, buy should still be enjoyable.