Upvote:5
A visitor application must be refused if a criminal conviction occurs within the last 12 months of the application under UK Immigration Rules:
9.4.4. An application for entry clearance or permission to enter under Appendix V: Visitor, or where a person is seeking entry on arrival in the UK for a stay for less than 6 months, must be refused where the applicant:
[...]
(b) has been convicted of a criminal offence in the UK or overseas for which they have received a non-custodial sentence, or received an out-of-court disposal that is recorded on their criminal record, unless more than 12 months have passed since the date of conviction.
For other categories, there is no mandatory refusal period of 12 months.
But in all cases, the officer has the discretionary power to refuse an application due to a previous criminal conviction regardless how long ago it was.