This is totally up to you and there is no legal requirement for you to disclose that you are disabled or provide medical evidence to prove this. In fact, in the context of job applications, any unnecessary enquiries about health or disability might fall foul of the Equality Act 2010 rules prohibiting pre-employment health questions.

With that being said, providing medical evidence of your autism may be helpful when asking for reasonable adjustments to be made both when applying for jobs and whilst in work. This is because an employer is not under a duty to make reasonable adjustments if it does not know, and reasonably could not be expected to know that an employee has a disability and that this is liable to disadvantage them substantially. 

Whilst employers are expected to take reasonable steps and have systems in place to find out whether reasonable adjustments should be made, there will be no question that the duty has arisen if you are able to provide medical evidence that demonstrates you have autism and that you need adjustments to be made as a result. 

For further information, see our section on applying for work has more information on telling an employer that you are autistic.

Employers and work providers also have duties when an applicant or employee discloses that they are autistic, and when recruiting and managing autistic employees.