Can he apply for citizenship? Can he work in the Uk? What restrictions are there?

He applies for a Marriage Visa. The london office number is below:

London office: +44 (0)344 991 9222

Marriage Visa
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Spouses of UK citizens or permanent residents (mainly those with indefinite leave to remain) may come to the UK under marriage visa category, and are able to work as soon as a visa is granted. You will need to meet the following marriage visa requirements:

If you have been together for less than four years you are granted a marriage visa for a probationary period of two years. If you are still married and living together at the end of two years in the UK permanent residence (properly known as indefinite leave to remain) will usually be granted.

If you have been together for four years or more outside the UK and you have passed the Life in the UK test, you are eligible for indefinite leave to remain (permanent residence) in the UK without having to live in the UK for two years.

The UK citizen or permanent resident must have actually met their non-UK spouse. This is to prevent a situation that occurs sometimes in arranged marriages where the husband and wife have never met.

You must intend to live together permanently with your spouse in order to obtain a spouse visa.

You must possess sufficient funds to pay you and your spouse's living expenses and those of any dependants without claiming public funds. Public funds cover various benefits paid by the Government if you are currently looking for work, if you are on a low income and if you are in various other situations.

Accommodation for the couple, and any dependants, must be suitable and available.
Spouses seeking to come to the UK on the basis of marriage to a UK national should apply for entry clearance before entering the UK.

If you have a visa valid for six months or less in the UK you cannot change status to a spouse visa.
Children of the marriage who are under 18 years old are allowed entry to the UK as dependants, and can make their application at the same time as the main applicant.

After a total period of three years in the UK if you meet the residence requirements you may then apply for UK citizenship.