According to the Visacode (visa rules) a reservation of return transport is sufficient:
1. When applying for a uniform visa, the applicant shall present:
(a)documents indicating the purpose of the journey;
(b) documents in relation to accommodation, or proof of sufficient means to cover his accommodation;
(c) documents indicating that the applicant possesses sufficient means of subsistence both for the duration of the intended stay and for the return to his country of origin or residence, or for the transit to a third country into which he is certain to be admitted, or that he is in a position to acquire such means lawfully, in accordance with Article 5(1)(c) and (3) of the Schengen Borders Code;
(d)information enabling an assessment of the applicant’s intention to leave the territory of the Member States before the expiry of the visa applied for.
(...)
B. DOCUMENTATION ALLOWING FOR THE ASSESSMENT OF THE APPLICANT’S INTENTION TO LEAVE THE TERRITORY OF THE MEMBER STATES
1.reservation of or return or round ticket;
2. ....
Source:
http://eur-lex.europa.eu/legal-content/ ... 32009R0810
As far as a Schengenvisa is concerned a reservation from the UK (or India) into the Shengenareaa (France) and then into the UK should be sufficient. And as far as I know the UK visa rules also do not demand that you buy tickets but that less relevant for the French, they simply wish to see reservations for tickets that show that they will enter and leave France/Schengen-zone to any other area where they will be sure to have access to.
Just incase an embassy has some made up rules, double check on the embassy's website in question what they say. Or check with the optional service provider (TLS, VFS) which is more and more used but officially can be bypassed in favour of direct applications at the embassy (saving yourself a service fee).