Which roundabout is near Big Ben?

The 'roundabout' in front of the Houses of Parliament is actually a square - Parliament Square.

You don't say how you are travelling, but I presume by train. Trains from Gatwick terminate at Victoria railway station or via the Thameslink route to Kings Cross. To be honest, the quickest and easiest way of doing the journey is to get the train to Kings Cross, which takes 45 minutes. Kings Cross Thameslink station is only a 5-10 minute walk from St Pancras, which is the mainline station to the East Midlands.

If you are determined to travel by road between Victoria and St Pancras, it is easiest done by taxi - just ask the driver to go via Parliament Square. There is a bus from Victoria to Kings Cross (the 73) but it does not go via Parliament Square, so you would have to get two buses, for example the 24 to Warren Street station then change onto a bus going eastbound to Kings Cross such as the 10. This will take an hour or so.

If you go by Thameslink through to Kings Cross, you will also get good views, because the train crosses the river. Not of the Houses of Parliament, but St Paul's Cathedral, Tower Bridge and the city.

What do you mean by roundabout? The actual route around the Houses of Parliament? It's called Parliament square. To get a taxi from Gatwick to the East Midlands (which has an airport of its own...) would cost a huge amount of money and to go via central London is a stupid idea. Are you sure you know where you're staying/how big England actually is?

The closest "round-about" where you can see Big ben is Parliament Square. It is right there. There is no other round-about nearby.

well I can't tell you but what I can say is that if you're planning to see it by cab then a London cabbie will know. Their knowledge of London is staggering (unlike mine!)