The personal allowance set for still wine is 18 litres per person.
You do not need to pay any tax or duties on personal goods you bring into Great Britain as long as they are within your personal allowances.
If you go over your allowance you pay tax and duty on the total value of the goods, not just the value above the allowance.
In declaring by conduct, any applicable import VAT, customs and excise duty must be paid on goods and merchandise in baggage rules apply.
You can find a list of eligible goods for declaration by conduct here:
List of goods applicable to oral and by conduct declarations
You can find merchandise in baggage rules here:
Bringing commercial goods into Great Britain in your baggage
There are no limits on the amount of duty and/or tax paid alcohol that an individual can bring into the UK as long as they are for their own use or gifts and are transported by the individual in question.
If an individual brings in alcohol and HMRC suspects they may be for a commercial purpose, officers may question and check the goods in question.
From the information provided, you, as an individual can bring 18 litres only while any other individual or person, such as your wife, can import an 18 litres separately.
It is not possible to share the allowance between yourself and your wife, but you and your wife can individually bring in 18 litres of wine each.
If you bring goods for your personal use, or as gifts, from the EU into Great Britain in your accompanied luggage and you exceed the personal allowances you will need to declare the goods and pay tax and duty due on all the goods in the category in which you have exceeded the allowance, not just those that take you over that category of allowance.
You can find further information here:
Bringing goods into the UK for personal use