This post describes how to get an Indian tourist visa if you're a British citizen.

Option 1: E-Tourist Visa

As of 15th August 2015, India is offering tourist visas online for British citizens. This E-Tourist visa lasts just 30 days though, after which you'll either have get another one or leave India. Here's some information from www.global-gallivanting.com:

As of 15th August 2015 British and Irish Citizens will now be eligible for the E Tourist Visa!  They join citizens from the USA, Australia, Canada, New Zealand, most European countries are eligible to apply for the ETV. A total of 113 countries are now eligible and the scheme will now operate at 17 airports making it much easier to visit India for a short visit. The ETV will cost about £39 but it is only valid for 30 days. It is not extendable or convertible and you can only apply for 2 ETVs in one year. You must still apply for the visa before arriving by filling out an online application form (at least 4 days before you travel) and paying a fee.  You then collect your visa on arrival at one of the major airports in India.

To get one of these visas, go to https://indianvisaonline.gov.in/visa/info1.jsp and fill out the form. But if you're trying to get the visa more than a month ahead of time, you'll get an error message: "Date of journey should not be greater than 34 days from Today's Date". Best wait until you're nearer your travel date then.

Option 2: 6 month tourist visa

To get a visa longer than a month, you'll need to post your application and passport. You can find details at www.vfsglobal.com/India/UK.

Option 3: Just turn up in India... no, just kidding

Germans, Aussies, Kiwis, the Finnish, and the Japanese can simply get a visa when they arrive in India. But the British can't (perhaps because India is still miffed about colonisation?). Hopefully India will relax their visa rules in the near future.