Will it be a good decision to do Bachelors in civil engineering from UK rather than India?

The answer is - contact your supervisor. Some universities also share the process to getting your PhD funded by the university. You must contact your PhD supervisor for the same, in most cases, a PhD scholarship is awarded at the time of accepting your application. If you don't get a scholarship from your university, you can also apply for an external PhD scholarship in UK. The process to apply for each scholarship is to visit their respective websites and follow the steps as indicated. 

Yes, you can get a 100% PhD scholarship in  the UK. You need to attach a good Statement of Purpose (SOP) and research proposal to the professor in UK you are willing to work with. Some  famous fully funded PhD scholarships in the UK are Leeds Doctoral Scholarships, Priestly PhD Scholarships, President's PhD scholarships and Carnegie PhD Scholarship. 

It is smart to have backup  plans. Apply to several universities and not just one. Getting into your top choice isn't guaranteed because many students apply and competition is tough. Having other options saves you time and stress if your first choice says no.

The UCAS applications for the UG courses in the UK open in the month of May. While the deadline to submit the applications for most colleges and universities falls on or around September 03. Deadlines for the University of Oxford and most courses in medicine falls near October 15.  

The earlier you start preparing for the fall intake in UK, the better. Get your test scores, documents, finances and other related requirements ready well before the admission applications commence. You must start at least 15 months before the desired intake. You should also be prepared with complete information on your finances/scholarships/loans.