Documents required from U.K. if applying for Visitor (Someone is calling from U.K.)-

Scanned Copy of Invitation letter from Son/ Brother addressing to The Visa Officer, British High Commission, New Delhi mentioning the purpose and Duration of stay along with the Names and Passport details of the Persons invited.
Employment proof – last 6 months bank statements, along with last 6 months pay slips.
Accommodation Proof- Rent Agreement.
Invitee’s Copy of Passport+ valid U.K. Visa.

Fast Track Service

The UK Border Agency will expedite the processing of your visa application and return of your documents. Customers may request this service if they are applying for a visitor visa (excluding student visas) and have travelled without difficulty in the last five years to one of the following countries: UK, US, Australia, New Zealand, Canada or a Schengen country.

Please note: If you have been refused a visa for any one of these countries or overstayed your visa to the UK or been removed or otherwise been required to leave the UK, the processing of your application is likely to take longer than the processing times set out below, and is unsuitable for the Fast Track process.

a valid visa for entry to Australia, Canada, New Zealand or the United States of America and a valid airline ticket for travel via the United Kingdom as part of a journey from the country in respect of which the visa is held to another country or territory;
a valid airline ticket for travel via the United Kingdom as part of a journey from Australia, Canada, New Zealand or the United States of America to another country or territory, provided that the transit passenger does not seek to transit the United Kingdom on a date more than six months from the date on which he last entered Australia, Canada, New Zealand or the United States of America with a valid visa for entry to that country;
a valid USA I-551 Permanent Resident Card issued on or after 21st April 1998;
a valid Canadian Permanent Resident Card issued on or after 28th June 2002;
a valid common format Category D visa for entry to an EEA State;
a valid common format residence permit issued by an EEA State pursuant to Council Regulation (EC) No. 1030/2002;
a diplomatic or service passport issued by the People’s Republic of China; or
a diplomatic or official passport issued by India; or,
a diplomatic or official passport issued by Vietnam.

Notes:

A valid U.S. immigrant visa packet (form 155A/155B)is a ‘valid visa for DATV exemption purposes.
An expired I-551 Permanent Resident Card issued on or after 21 April 1998 when accompanied by an I-797 letter issued by the Bureau of Citizenship authorizing its extension, exempts the holder from the DATV requirement.
Holding either an I-512 Parole letter or an I-797C (Notice of Action) instead of a valid U.S. visa; or a Transportation Letter instead of a valid U.S. Permanent Residence Card issued on or after 21 April 1998; or a U.S Visa Foil endorsed, “NOT A VISA. FOIL PREPARED AT DHS REQUEST” does NOT qualify for exemption from the DAT visa requirement.
Holding a valid travel document with a U.S. ADIT stamp worded – “Processed for I-551. TEMPORARY EVIDENCE OF LAWFUL ADMISSION FOR PERMANENT RESIDENCE VALID UNTIL…. EMPLOYMENT AUTHORIZED” does NOT qualify for exemption from the DAT visa requirement.
Whether holders of non-national (including refugee travel documents) require a DATV depends on their nationality and whether they qualify for one of the exemptions listed above. So, for instance, the holder of a non-national travel document (e.g. a refugee travel document) who is a national or a citizen of one of the countries listed on the DATV list (e.g. Afghanistan) will require a direct airside transit visa if they are traveling to the UK to transit on to a third country.

Visa requirements same as tourist additional requirement
1 visa from VAF-6 for (DATV)
Visa for next destination and Ticket details

Longer term multiple entry (1 to 2 years): Rs. 23,650/- , £ 278

Longer term multiple entry (5 years): Rs. 43,450/- , £ 511

Longer term multiple entry (10 years): Rs. 62,650/- , £ 737

Direct Airside Transit Visa, In Transit Visit, Join Ship or Aircraft: Rs. 4,600/- , £ 54

Special visitor – Student visitor, up to 6 months: Rs. 6,800/- , £ 80

Returing Resident: Rs. 23,650/- , £ 278

Visa for any other purpose (includes employment,HSMP,UK ancestry) and Certificate Of Entitlement: Rs. 23,650/-, £ 278

Single Entry Visa to Replace Biometric Residence Permit Overseas: Rs. 6,150/- , £ 72

Forwarding documents to Commonwealth Countries / Overseas Territories (additional fee): Rs. 5,950/- , £ 70

Handling applications on behalf of Commonwealth Countries / Overseas Territories: Rs. 4,250/- , £ 50

Transit : Rs. 3950.00 + 100 cash payment charges

Direct Airside Transit Visa (DATV): Rs. 3950.00 + 100 cash payment charges

Business: 15-30 working days for first time travelers (Discretion of Embassy)

Transit: 15-30 working days for first time travelers (Discretion of Embassy)

Direct Airside Transit Visa (DATV): 15-30 working days for first time travelers (Discretion of Embassy)