If British people use only British services and shops,? would other shops close, and British people get jobs to support their family's?

Certainly that would work. Unfortunately other countries would do the same and our whole banking system would collapse as they refused to trade with us.

Import/export would fail leading to massive food failure, drug supply failure, raw materials failure.

Pretty much an apocalyptic event. The world is connected, we cannot supply our own needs.

Nearly all the manufactured goods we use and more than half of all the food we eat comes from abroad. If we stopped buying foreign goods and produce, we'd have to expand our manufacturing industry and agriculture giving more jobs to people in this country, but our labour laws mean that prices would double so we'd have to work harder just to survive. What's more, we can't fill our vacancies now because people lack the skills and inclination to do the available work. If it wasn't for immigrant labour and immigrant businesses, our country would grind to a halt. Mass immigration is a symptom, not a problem. If the racists and jingoists would get off their backsides and put in some effort, this country wouldn't seem so much like paradise to overworked Asians and East Europeans.