Screwfix sell cheap JSP Force 8 respirators for which you can purchase P3 filters, or ABEK1P3 filters. Alternatively, I believe they also sell 3M series respirators which have a much larger range of filters, from standard P3 filters up to ABEK2P3, which are around £30 per pair. The 3M 7500 series are the most comfortable in my opinion, have a sweat drain, and also a downward facing exhale valve to stop misting up. Just make sure you do the suction test for the JSP respirator, or the bulge test for the 3M before entering hazardous areas.