This an excerpt (with stress added by VE) from this document:
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/220968/foi_eumembership_trade.pdf#page=8from
"2) Agriculture
Although barriers to trade between Member States have been removed, agriculture is probably the most protected sector in the European Union interms of external barriers, through the Common Agricultural Policy (CAP).
The costs of protectionism in this sector are possibly the most damaging to economic welfare and provide a good illustration of why the UK should remain a force for more outward-looking reforms in the EU.
At the broadest level, it is estimated that the CAP costs EU citizens roughly €100 billion a year: €50 billion to consumers through higher food prices and €50 billion to the taxpayer. The UK, as a net food importer, suffers particularly from higher food prices, impacting both on the consumer and on the food processing industry, which accounts for around 7% of GDP [Philippidis?]. Minford et al (2005) estimated that the CAP costs the UK 0.5% of GDP, and in economic and budgetary terms is probably the most costly factor of EU
membership.
These costs arise in a number of different ways, and have different effects.
The most significant economic distortion occurs through market price support, in the form of border protection (tariffs and import quotas), keeping cheap imports out and permitting artificially high prices12. The results are manifold: welfare losses to consumers who pay a high cost through higher prices, resources diverted to agriculture from more productive sectors of the economy,
and losses to third country producers through lack of access to markets and depressed (and volatile) prices.
The second element of protection arises through budgetary transfers (of the order of €30 billion) in the form of direct payments to farmers. Having said this, in June 2003 and April 2004, the EU agreed reforms to break the link between production and receipt of payments for many important products, albeit with some scope for a continuation of the status quo.
Surplus produce is subsidised (the third element) and „dumped‟ on third markets."