The University of London will grant certain recognised qualifications automatic exemption. One important point to note that in order to be considered, your Polytechnic Diploma must have been completed within the last 5 years.
If you have any of the following qualifications and or their equivalent you may be eligible for up to 4 unit exemptions. In order to maximise your exemptions you may need to take the short SAA-GE Bridging courses in Mathematics and Economics.
Full details on the exemptions can be found here.