Can I get a full refund on a flight to Japan?

My wife, son, Japanese daughter-in-law and I were due to fly to Japan next weekend for a holiday

Unfortunately that's not how it works. Were you booked on a package holiday to a destination that the Foreign Office subsequently rules off-limits, then you would certainly be entitled to a full refund. However, airlines are not obliged to operate the same policy.

British Airways (along with Virgin Atlantic, ANA and Japan Airlines) continues to fly from Heathrow to Tokyo. It will satisfy its contract to deliver you safely to the Japanese capital; the fact that you no longer want to go carries no legal weight.

However, BA and other airlines are going beyond their usual obligations by offering a range of options for travellers booked to Tokyo in the next few days and weeks, including postponing the trip or switching to a different destination.

BA has been offering full refunds to Tokyo passengers over the past week, because it has changed the routing of its flights and added a stop in Hong Kong, extending the journey.

So my advice is this: wait a few more days. You will still have the option to postpone or switch destination but you may also find that you qualify for a full refund.