In general, a service provider should wait and give you time to speak, if they would listen to someone speaking fluently. This applies whether they are a shop assistant, a person speaking to you on the phone, or anyone else providing a service.
For particular examples, see Examples on stammering: Services and public functions.
Discrimination arising from disability
If a service provider fails to give time to speak, this is usually likely to be a breach of the Equality Act as discrimination arising from disability, unless the service provider can show objective justification (below), or possibly the ‘lack of knowledge’ defence (below). As discussed below, it is likely that those defences will very often not apply.
Because of how discrimination arising from disability, is defined, it does not matter whether the service provider would act in the same way to a non-disabled person who was taking some time, or or who was speaking in an unusual way.
Objective justification defence
The service provider has a defence if it shows objective justification. In outline, this involves showing that their action was a proportionate means of achieving a legitimate aim.
However, showing justification will normally be difficult in this situation. The service provider would probably need to show not only a legitimate aim, a real need, but also that it could not have achieved the aim in a less discriminatory way, and that the aim was sufficiently important to outweigh the discriminatory effect.
A customer with a stammer has difficulty in explaining to a bank cashier what his service requirements are. The cashier asks the customer to go to the back of the queue so as not to delay other customers waiting to be served. It seems likely that this would normally be a breach of the Equality Act.
More on this example, including the justification defence: Example: Queue in bank
A person who stammers phones a restaurant to book a table. They are struggling to speak, and the restaurant puts the phone down. This is likely to be a breach of the Equality Act.
More on this example, including the justification defence: Example: restaurant puts phone down
There will be some situations where not giving someone time to say what they want could be justified, such as in some emergency situations. It would be for the courts to draw the boundaries.
‘Lack of knowledge’ defence
The service provider also has a potential defence if it did not know of the disability and could not reasonably be expected to know. However, that seems unlikely to apply in most cases where the individual is having difficulty communicating.
Other types of claim
Other types of claim under the Equality Act could also apply here. In some cases there will be direct discrimination for which there is no objective justification defence. It could be direct discrimination if, because of the stammer, the service provider treats the person worse than they would treat someone else who is taking longer to communicate.
The reasonable adjustment duty could also apply in some cases.
Can service provider require use of an alternative to speaking?
Can a service provider insist that a person who stammers write down what they want to say, or get someone else to phone or speak on their behalf, or to email in?
If the person who stammers would prefer to speak themself, this is likely to be subjecting the person to a detriment within s.29 EqA. Assuming it is not direct discrimination, the service provider will have a defence if they show objective justification, namely that it is a proportionate means of achieving a legitimate aim. However, as outlined above the objective justification test is not an easy one to meet. It will depend on the facts, but in most cases a service provider would probably find it difficult to show objective justification for not allowing the person to speak.
The previous paragraph assumes a claim for discrimination arising from disability, where the objective justification defence applies. The reasonable adjustment duty may also be relevant. If the alternative put forward by the service provider involves a cost to the customer, note that under s.20(7) EqA a person subject to the reasonable adjustment duty is not entitled to require the disabled person to pay to any of the costs of complying with the duty (unless the law expressly says otherwise.)
On inviting someone to write a note as an alternative to speech, see also Making services accessible: Writing notes?