Can you gain admissions to a top UK Engineering PhD program with limited research?
You are not expected to have any research publications at all to enter a UK PhD programme, even at Oxbridge. Any you have will put you in good stead. Most entrants to UK PhD programmes come from an undergraduate course or a masters programme where they have learnt lots but only undertaken research within limited parameters. Many will have only completed a project and written an unpublished report.
A first class undergraduate degree, a 2:1 is sometimes acceptable; but because undergraduate scoring is not standardized across UK (or worldwide) universities there will be an extended interview. You will need to be able to demonstrate your knowledge and your capacity to reason with a good performance during the interview(s) with your prospective supervisor and probably others in the department. The interview is also an important chance for you and your supervisor to find out if the two of you will be able to work together closely in the future.