持有半年的英国访友签证可以在英国境内续签吗

据我所知这种签证不能在英国境内续签，只能回中国签。曾有朋友尝试过，还是预约的面签，结果被告知除非非常特殊的情况（例如在英国突发大病无法登机等），这种签证不能在英国境内续签，只能回居住国签证。而且1年内访问签证不能在英国居住超过6个月，所以你如果之前的签证已经居住了6个月，有可能马上再签证的话未必会拿得到签证。

http://www.ukba.homeoffice.gov.uk/visas-immigration/while-in-uk/extending-stay/
If you currently have temporary permission to stay in the UK, you may be able to extend this permission and stay here longer. If you came here as a visitor, you cannot extend your permission to stay as a visitor beyond 6 months in most cases - however, in some circumstances you may be able to switch into a different immigration category.

depends on what types of visa you are going to apply I think.
www.ukba.homeoffice.gov.uk could be a website you may feel useful

我也想知道可以续签吗

我也想知道可以续签吗