As an Aussie who's lived in England for thirty years I can tell you that a perfect Summer day is here. From where I've come from (38C regularly in summer, anyone?) these temperatures don't sound too bad. But nothing here is geared up for heat. It's all about keeping the warm in, because that's what we usually deal with.
A couple of suggestions. During the day keep the curtain closed and the windows closed and at night open everything up. That keeps the heat out during the day and helps keep the air flowing through in the evening. I realise it isn't practical for everyone, but if you can it's quite effective.
On a personal level ban any synthetic fibres. They talk about linen being cool, but cotton is cooler. A small spray bottle filled with water, squirted over any exposed parts a lot is really helpful.
And remember. It won't last.
I lived in the North East for five years. My children were born there and I absolutely love that part of the world. But my god. You couldn't go anywhere, even at the height of Summer without a jacket. Brrrrr.
In the meantime, I am rejoicing at sitting outside in the garden at 8.30, without a jacket, and I'm not cold at all.