What to wear at a jubilee garden party

[chocohen]

Ok I'm really chuffed that I got some tickets to take my mum to the jubilee garden party at stormont belfast.
However, now the initial excitement has settled I am now wondering what do you wear to a garden party.
Please can any of you help me decide?

Sunday best (can be floaty), probably with jacket. Nice hat! Minimal/no black. Comfy shoes!

What you would wear to a wedding. But comfy shoes v important I would imagine.

Thanks. I was worried I might have to wear a hat as I don't suit them. Drat