Upvote:0
If you need a visa for the UK (you can easily check on https://www.gov.uk/check-uk-visa) you must apply and your application must be approved before you travel to and arrive in the UK.
AFAIK Visa are NOT issued on arrival.
Upvote:2
Neither the UK nor the Schengen area (which includes France) issues visas on arrival. Whichever way you're travelling, if your wife needs a visa, she needs to get it before you set off.