这个180天我最近确实查了一下，但是不是那么明确的：
"People holding visit visas can only remain in the UK for a maximum of six months on any one visit, or until the visa expires if less than six months. This restriction is indicated on the visa by the entry ‘180’ days after the ‘Duration of stay’ section. "
这里面说了最多六个月，也说了180天。
还有一个地方也只提到了6个月。
Entry clearance endorsements Visa nationals
C:VISIT: 6 MONTHS
另外一个地方也提到了6个月：
How long is leave to enter normally granted for?
Genuinely be seeking entry as a general visitor for a period not exceeding six months, or 12 months for a visitor accompanying an academic visitor (who is a child, spouse or partner).