No your right I haven't been to every medical establishment in the country that would not be possible so I base my assumptions on what I have personally experienced.
There are extremes in the system from a rural practice with few patients to city based practices who are dealing with high populations and localised social problems.
Why do we have so many more foreign workers now in the NHS it's because the people born and trained in the UK are disillusioned and fed up with the poor management and obvious wastage in the NHS and moved on most reluctantly to bigger and better things.
With some current NHS staff unable to understand or speak English as you stated the situation can only get worse with more mistakes and an increase in medical claims against the NHS which are at a all time high.
The NHS as we know it needs major surgery immediately or it will implode on its self with disastrous consequences for the country.