According Official List of documents for UK Visitor visa there is no fixed amount you must have to apply the visa. But it is a general rule that visa applicants must have enough money to support and accommodate themselves without working or help from public funds, or they and any dependants will be supported and accommodated by relatives or friends:
Section 2: other documents you may want to provide – all visitors
Financial documents showing that you have sufficient funds available.
These must clearly show that you have access to the funds, such as:
- bank statements
- building society book
- proof of earnings such as a letter from employer confirming employment details (start date of employment, salary, role, company
- where a third party (who is either in the UK or who will be legally in the UK at the time of your visit) is providing financial support to
you e.g. a business, a friend or a relative, documents to show they
have sufficient resources to support you in addition to themselves and
any dependant family should be provided
So you should ask in UK Embassy for this, and they'll decide by themselves, as this is very dependent of many factors. I think that about 200 GBP per day will be OK, but can't say for sure.