OK.
I think I got what you meant with this. Let me put it all together -
Access to £50,000 -
1) If you have money in your UK bank account - can show bank statement.
2) If you know someone, who's got the money in UK bank account - Then Bank letter, declaration and sign verification will be required.
3) If you have money in overseas bank account or if you know anyone who's got money in overseas bank account - then again Bank letter, declaration and sign verification will be required.
All the above 3 routes can be added together in case to show prove £50,000 access.
I appreciate your help and It means a lot for me now. Please confirm if I have got everything correct this time.