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My Guessometer says you will need around £800/month.

1 trip once a month to Europe? (weekend, lets say 1 night only):
- Hotel: £60 (quite cheap)
- Flight: it really depends, but lets say £100.
- Food: £100 ( you don't want to eat sandwiches only, do you?)
Which is £260/month.

Social life, lets say you go out 4 times a week, 2 pub crawls 2 restaurants:
- Pub: 3 or 4 drinks: £15.
- Restaurant: £50 .
which is £65/week or £260/month.

Lets add up: £1320.

Add utilities, food, transport, council tax, etc: £400/month (feels optimistic).

Grand total: £1720.

Or £20640/year.

Supposing 1/3rd of your income goes to the taxman you would need around £29000/year to have the amount above in your pocket.

This is a very off the cuff assessment, but I don;t think it is too far off from the truth.