I seriously doubt it, as American lights would expect to run on american voltage, which is 110 as opposed to our 240. You need a transformer, which you should be able to get fairly easily.
The previous response is quite correct, that if indeed the lights are rated at 110V which is the norm in the USA then you would need a transformer to reduce 240V down to 110V. One of these would probably set you back around �20 max, however you will need to find out first the exact rating of the bulbs in total so that the transformer can cope with the loading. My guess is it'd be cheaper to just buy english, unless they are very expensive lights.
I was going to suggest you could just replace the bulbs with some that run on twice the voltage, but mature reflection says this is dangerous territory. You really don't want to inflict 240 volts mains on a wiring set whose insulation is only intended for 110 volts.
If you plug your 110volt lamps into 240volt UK supply the lamps will instantly blow. You need a transformer to reduce the voltage. You can get one from Maplins.co.uk
as a person who travels to the USA and purchases dozens od stings of outside Xmas lights, this is the way I wire in 110 volt lights. I purchase a 240/110 volt 5 kw double plug transformer from a local electrical. I have now two. I have purchased from the USA four good quality extension leads with four american sockets on each lead. I cut off the one end so removing the single american two pin plug. I wire this end into a junction box and then wire into the transformer. American Xmas lights are designed so you can string three sets of lights end to end. Make sure the connections and junction box is kept dry and away from young children. This has worked well for over ten years and the lights are better than anything you buy in the UK.