For Imperial, getting as many 8s and 9s is advantageous. Most applicants will have a majority of 9s and 8s for Imperial. Also you should look at Cambridge, UCL, KCL, QMUL, Durham, Royal Holloway, Bristol, Warwick, Manchester, Nottingham, Reading and others.
Maths, Physics, Chemistry and Biology should be 7s ideally for Imperial, at minimum. UCL love to care about language GCSEs, but you should be fine as long as you have above a 6.