"Starvation"? First, tariffs = higher prices, not complete blockage. Second, import tariffs are taxes imposed by the UK, and they can unilaterally remove them at any time - they just don't want to.

In a no-deal brexit, there may be a short period of time where the chaos causes various shortages. But this'll be things like a lack of some fresh fruit, not starvation. The market will figure out solutions quickly, and demand will be met. Though probably there will be higher prices and lower quality until/unless the UK sorts out their trade and regulation issues; if they insist on maintaining the EU's ultra-high-regulation environment, then they're going to find trade deals very difficult, and it also increases domestic prices.

I still think they'll cancel brexit at the last minute, though.