what crops can I plant now (july)

Hi Tarquin,
The easiest way to find out what will grow this time of year is to look on the back of seed packets. I know lettuce, radish, small salad crops etc. will grow.
Hope this helps, and welcome to GoY. :~))

I'd try beetroot, especially the coloured ones, yellow, pink and white, as baby beet, carrots (early varieties which will grow by the autumn), Chinese greens, especially of the 'cut and come again' variety like mizuna greens, black radish or any other winter radish (makes large mild roots like turnips) baby turnips like 'Long de Croissy' or the little white ones.
All of these may be sown now.

You can add spinach beet to Bertie's list. It is a quick growing leaf crop.