UK tourist visa - Marriage certificate

I've had important documents such as a birth certificate laminated before and it did cause problems. It should be accepted as it doesn't have to be stamped or anything. If you want to get a copy as laminated documents make it really hard to detect important security features.

On a side note I found this on the UK GOV website relating to a passport application:

IPS regional offices have a very small percentage of applications supported by laminated documents. Documents that are laminated are usually birth certificates, marriage certificates and naturalisation/registration certificates.

IPS examiners cannot be sure that the laminated documents submitted with an application are genuine.

Major concerns regarding laminated documents are that watermarks cannot be easily distinguished, nor can the quality of the paper be felt, and with naturalisation/registration certificate the security features such as the heat reactive number cannot be utilised.

Laminated documents must not be accepted in support of passport applications, unless in cases covered by the exceptions shown below. Examiners must request unlaminated versions of the documents submitted.

Whilst that is relating to passports it shows the UK can be strict on laminated documents so it might be better to request a un-laminated copy.