Refer to the new role for “proof of funds”. You MUST provide a bank statement(s) showing all transaction for the last six months at least, and confirming the current balance with a bank statement. Moreover, the current balance should be equivalent to the minimum required Funds at the time you send the application.
Now, A letter of solvency providing the current balance of your accounts(s) or the average credits and debits in your account(s) is not acceptable evidence anymore for the Visa office .
For more information you have to check the “Visa Specification Instructions” guide.
Good luck.