Kitchen tap Connection to mains issue

[Adam tl]

Hi, I am replacing a kitchen tap and have run into some trouble when connecting the flexi hot and cold pipes to the hot and cold mains pipes. The connection end of the flexi pipe from the tap is a15mm, however the mains pipe I need to connect to is a 12mm. What connector do I need to buy? So far have only found reducers and couplers with either the same female to female ends, and the same diameter ends.

Thank you,
Adam