No reputable company will tint the front windows for this very reason. They would be liable if they modified your vehicle in such a way as to make it illegal.I think you'll find the front windows have as much tint as legally allowed in the UK. Any darker and you risk being stopped by the police. Even clear glass has a "tint" as it only allows about 85-90% of light to pass through.
https://www.gov.uk/tinted-vehicle-window-rules
Take your van to primo tint or probably any tinting company, they should have a light meter to measure the tint that's there already.I've just had a reply from Primo Tint saying the same, I just need to find images of max legal tint now!
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