check with the nso, dont jeopardize your visa application, they will certainly look for proofs
http://www.ukvisas.gov.uk/en/ecg/set...ncees#18013077
SET1.15 What evidence is required to prove freedom to marry?
For single adults, the Registrar normally accepts the parties’ declaration that they are free to marry. The ECO should, therefore, accept a similar verbal statement by an applicant, together with any supporting correspondence from the person he/she is going to marry. This is unless there are strong grounds to believe that one of the parties is still married/in a civil partnership or has been married/in a civil partnership previously and is concealing this fact. In such cases the ECO should make whatever enquiries as seem appropriate.
The ECO should warn anyone going to the United Kingdom for marriage who has previously been married/in a civil partnership that he/she may be required to provide the Registrar with evidence of freedom to marry before the Registrar can accept a notice of marriage.
Where the ECO has doubts about an applicant’s intention to marry, the ECO should ask to see evidence of freedom to marry before issuing an entry clearance:
Widowed person: death certificate of the late spouse.
Surviving civil partner: death certificate of the deceased civil partner.
Divorced person: evidence of divorce eg a divorce certificate. NB for the UK this is a decree absolute divorce certificate - this is stated on the order from the Family Court. A person is not legally divorced until the decree absolute is issued. A decree nisi is not acceptable evidence.