Santander Dividend Re-investment Plan (DRIP)

I hold a small amount of Santander shares and have taken the option to have any dividends used to purchase further shares with Santander under the Santander Dividend Re-Investment Plan (DRIP). Gross dividends have Spanish Withholding Taxes deducted before being used to purchase further shares. Does this have to be included in my Self Assessment.

Hi Gillian Smith,
If,  the company reinvests the dividends by using them to purchase additional shares on a shareholders’ behalf through a dividend reinvestment plan (DRIP) (the company reinvests the shares automatically, without the shareholder having to do a thing or ever receiving the dividends physically themselves), that shareholder does not pay income tax on the reinvested dividends until they eventually sell the shares. 
Thank you.