Tax deduction query re allowable expenses

If the revenue disallow a portion of your expenses e.g. phone etc from working at home (1/3 for personal use) are they likely to deduct a portion of the capital purchase of a smart phone / tab / computer for personal usage?

It's not that "Revenue disallow" anything, unless you get an audit. The system is self assessment so you have to determine the business element of your expenses, and also the business use of capital assets.

I presume since you've distinguished that the above items are capital purchases, that the tax treatment is different to ordinary purchases - capital allowances (tax depreciation) rather than an expense. So if the asset is used 50% for business then you are allowed 50% of the capital allowance as a deduction.

Hope that makes sense!

Incidental personal use is acceptable.

Buy the items as 100% business and disallow an element of the ongoing cost (if you deem it to be more than incidental).