If you are re-entering the UK and you wish to apply for a Tier 1 or Tier 2 visa category, it is advised that you carry some form of documentation to evidence your intentions.
This could be an offer of employment, or a Certificate of Sponsorship (COS), or evidence of your Tier 1 Graduate Entrepreneur endorsement.
Similarly, if you are due to start a new course of study as a Tier 4 student, be aware that you cannot apply in the UK if you have not completed your previous course of studies. We advise that you carry evidence of your new course such as a print out of a CAS statement or offer letter. You should also carry evidence to show that you can afford your new course of study and the living expenses (such as a bank statement).
Where you have an offer of further studies or work in the UK, you should be able to explain in detail that you will be applying for the visa, how you meet the requirements of that visa and potentially be able to show documentation which confirms this as well as explain a timeline before your visa's expiry date by which you will be making your application.
For further information about application processes and required documents for applying for work category visas, please refer to our working in the UK after your studies page.
There remain a very small number of cases over a period of years, where people have still been refused re-entry.
If you wish to avoid taking any risks, our best advice is that you avoid non-essential travel outside of the UK and complete any visa application processes before making further trips.