How much monthly pocket money does the husband have to give to his wife according to Islam? Basically, what is the wife's nafqa in UK currency?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
Islām enjoins on the husband to provide for the wife and children. The basis of this obligation are the following verses:
(Sūrah “Lodge them where you lodge according to your means, and do not injure them in order that you may straighten them; and if they are pregnant, spend on them until they lay down their burden; then if they suckle for you, give them their recompense and enjoin one another among you to do good; and if you disagree, another (woman) shall suckle for him..”al-Talāq: 6)
“but the father of the child shall bear the cost of the mother’s food and clothing on a reasonable basis” (Sūrah al-Baqarah: 233)
The Messenger of Allāh (May the peace and blessings of Allāh be upon him) said:
“They have right upon you for their maintenance and clothing” (Abū Dawūd)
He also said to the wife of Abū Sufyan:
“Take what is sufficient for you and your child on a reasonable basis.” (Reported by al-Bukhāri)”
As for your question about a monthly allowance, then there is no specific amount and it will depend on local custom.
Only Allah knows best
Written by Imam Abdul-Malik Sheikh
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Al-Ikhtiyar Li Ta’lil al-Mukhtār Vol.4 p.3