Im not a medal expert, so cant give a definitive answer, but I'm not really aware that there have been any copies made, due in the main to the relatively low value of the medal. The only one regularly copied is the Air Crew Europe Star which carries a value of around £150 to £175 plus depending on provenance.
But its difficult to actually define a copy. I had three Uncles who served in WW2 in one branch of the family, their elder brother being my Grandfather. When he died, my grandmother threw away his medals sadly, so they are missing. The next brother had his tucked away, which I found when I cleared his flat upon his death. They were 'original' as issued at the end of the war. The third brother was an original member of the SAS and the only one to win gallantry medals, which he has 'somewhere lying around'!
However, the fourth brother never claimed his, so I did about ten years ago. As he was never given them at the end of the war (which they confirmed) they were sent to me free of charge. Interestingly, the box, complete with its prepaid postmark is identical to the second brothers, including a Kings Crown stamp! The medals (a war medal and couple of stars) are all modern manufacture, and in fact look more copper in colour than brass (new copper), while the ribbons are definately much brighter in colour.
As these are official Ministry of Defence issue can they be classed as copies? They are obviously not wartime manufacture, but as medals were are are still being produced, how do you class them? Ribbons might be some modern material like polyester, but again all official issue, possibly made by the original company.
As I say, Im not aware of copies other than the ACE, which has noticable differences.
It well be worth having a look within www.britishmedalforum.com as the subject of Battle of Britain bars has been covered there on a number of occasions. Original bars have been commanding 4 figure values for some time now, and this has led to numerous copies appearing on the market. Regarding the medals themselves, Alexís point is well made, how you classify modern manufactured medals issued from the Governmentís Medal Office. Not withstanding that point, which I am not going to attempt, virtually every British medal and award that has ever been issued is copied; some for decades now.
Buying medals is about provenance, groups with named medals are to some the starting point, as is supporting documentation and other paperwork. However itís worth taking into account copy medals can be named and therefore groups created from a few bits of paperwork or a well researched log book.
There are a lot of excellent books on the subject, and within the UK there are numerous medals societies including the Orders and Medals Research Society (ORMS) www.omrs.org.uk
Glenn, reading Hyltons posting, I realised I hadnt commented on the bar.
As he says, the bar itself commands a large sum as relatively few were awarded. As such probably the best way to get a genuine bar is with a group and full provenance, most others will be suspect and very hard to find under a large price.
Saying that, a friend of mine picked up the paper envelope for a BoB bar for a few quid, and later the bar itself very cheaply, which he had checked at Spinks (the Medal Dealers) as genuine.
One way of discounting many fakes straight off, is the fact that the four holes on the corners are usually off centre. Genuine ones have holes placed very precisely within the circular decorated border. But that only discounts the cheaper ones, its not hard for a repro to be made with more accurate holes.