It does make sense for a service provider, in deciding whether to offer an adjustment, to try and distinguish whether or not a customer who stammers has a ‘disability’ within the Equality Act. This page says why. For a summary on accessibility for customers who stammer, see Making services accessible.
In practice, a service provider should assume that any stammer falls within the Equality Act 2010:
It makes good business and customer service sense. Hopefully no organisation wants their service to be inaccessible, or difficult to access, for someone who stammers (or to others with a speech disorder). Nor does it wants its staff being rude to a customer because of a stammer. This is so whether or not the stammer is substantial enough to be a ‘disability’ within the Equality Act.
Assuming that any stammer falls within the Equality Act also makes sense in terms of ensuring that a business complies with the Act and is not sued for compensation under it.
Legally a stammer may not be a ‘disability’ within the Equality Act if it has only a minor or trivial effect. In practice this may be rather a theoretical possibility, but even if there are stammers which do not have the legally required effect, in practice the member of staff dealing with the customer cannot know whether this is the case. A stammer may seem minor at the particular time, but there are several ways in which it could still be a ‘disability’ within the Equality Act. For example, the stammer could be (and quite likely is) more severe in other situations. Or the individual may be switching words and perhaps limiting how much they say, to try and minimise the extent that they stammer openly. In practice it should therefore be assumed that the stammer is within the Equality Act.
If a person who stammers is actually claiming compensation for discrimination, the service provider may want to look more closely at whether the particular stammer qualifies as a ‘disability’ under the Equality Act.
Old Code of Practice
The Revised Code of Practice – Rights of Access: services to the public, public authority functions, private clubs and premises issued by the Disability Rights Commission in 2006 commented at para 5.13:
Service providers seeking to avoid discrimination… should instruct their staff that their obligations under the Act extend to everyone who falls within the definition of ‘disability’ and not just to those who appear to be disabled. They may also decide that it would be prudent to instruct their staff not to attempt to make a fine judgement as to whether a particular individual falls within the statutory definition, but that they should focus instead on meeting the needs of each customer.
This Code of Practice is no longer in force but the advice seems equally valid today.