What type of jacket/coat to pack?
u cant go wrong wiv an umbrella and a trench coat
but i would advice you to bring something warm wiv ya, sometimes march can be freezing! =D
It will be the end of March so a trench and layers of sweaters? Will gloves be necessary?
london weather is as random as it gets. you probably won't need gloves, but bring an umbrella and sunglasses, you never know what you need. you should be fine with a trench or a blazer even as long as you can fit a sweater underneath. it could even be pretty warm, but you never know.
A foldable brolly works wonders. A waterproof jacket/trench will do great, cashmere sweaters keep you warm, tee shirts are always basic needs, and leather gloves should suffice. Don't forget boots and a good waterproof bag (i.e.LONGCHAMP!). And leave enough space for your shopping-loads of great shopping areas here in London.