The main bookshop foreign students go to is Darussalam Bookshop near Tayraan street off Mustafa An-Nahas street in Nasr City, Cairo. They have an English section with books usually 1/3rd of the price in the UK and also you can find quite a few Nahu (Arabic grammar) and Sarf Books there such as Al-Ajrumeeya and Nahu-Al- Waadih.
If you are looking for Arabic books only then best visit Al-Azhar i.e. the area close to Al-Azhar Mosque where there a tons of bookshops specialising in Islamic books.
And Allah knows best