Hello smartie, welcome to the forum.
What type of visa are you thinking about ?
Visitor Visa ?
Settlement Type Visa?
Or another?
All documents that are applicant mandatory according to immigration rules MUST be original (unless otherwise stated)
Some documents may be submitted as certified copies if provide with explanation and if acceptable to UKBA.
In general UKBA statePlease take a look at the UKBA Supporting Documents GuidanceAll supporting documents must be originals, not copies