The Government banned leaded (known as 4-star) petrol from general sale on the 1st January 2000. This was as a result of European legislation to reduce the amount of harmful emissions, including lead, from road traffic.
During the latter half of 1999, garages began switching to LRP (Lead Replacement Petrol) and by November it was basically impossible to buy leaded petrol anymore. As the years have passed this too has slowly been phased away and now it is only possible to buy unleaded petrol form mainstream garages.
No Capris were ever built that were suitable for using unleaded petrol directly from the factory. Do not believe anyone who says differently. However you can directly swap your cylinder head for a late model Sierra (1988-1990) which was fitted with an unleaded head (note the information on the next page) or alternatively have hardened valve inserts fitted. Budget around £200 if you take the head off yourself or £500 for the garage to do everything.
You must not run your unmodified Capri on unleaded fuel only. If you do not get your head converted or replaced then you must use a petrol additive (see later).
I started off using LRP in my Capri but I noticed a drop in performance and poor cold starting. After a couple of months I switched to unleaded using a 4-star replacement additive. In my case it was Redex 4-star replacement. This worked out cheaper than LRP even with the additive cost and the results were good.
In 2001 my Capri was taken off the road for a restoration and the cylinder head was removed and sent away to a specialist engineering shop. It has now had hardened valve seats inserted and will run off unleaded petrol permanently. However I still use the lead substitute additive as this enables the car to run without retarding the ignition which reduces both power and performance. This is still the situation over 30,000 miles later in 2021…