We all need to dress for work, however what you consider to be business workwear and what HMRC considers to be workwear, usually differs.
The main rule of thumb, is that if an item of clothing has dual purpose, then HMRC generally do not like it. That means any clothing which can be used both personally and in the business.
I.e. Whilst you may purchase some smart shirts for use in your business meetings, HMRC will not allow them as expenses if those same shirts are something that you could reasonably be seen wearing whilst out for a meal.
The easiest solution to this, is to ensure that anything you buy for business use, is branded with your business logo. As soon as it has your business branding, HMRC would accept that it is unlikely to be something you would wear in your personal life.
An important point here is that the logo/branding cannot be hidden, too small or removable.
A notable exception to the branding rule is when the clothing/footwear you are buying, is specialist protective clothing. Typically this means items of safety clothing such as high visibility vests and steel toe boots.