Introduce emergency legislation that reduces the speed limit for all 70mph and 60mph roads to 55mph. Make this time limited to the duration of the Russian invasion of Ukraine. Back this with a public information campaign positioning this as a national act of solidarity for the people of Ukraine.
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This will send a strong signal and could have a material impact on UK imports of Russian oil, which amount to 8% of our our oil demand; if we reduce demand enough we could in theory remove any need for Russian imports.
This could reduce inflows to the Russian economy, put pressure on Vladimir Putin and reduce Russia's economic ability to wage war.