Can I ask for an indication of what sentence I will receive?
Yes. There are procedures in both the Crown Court and in the Magistrates' Court for indicating a sentence in the event of a plea of guilty. There is no formal procedure for seeking an indication of what the sentence would be in the event of being found guilty at trial.
Advance Indication of Sentence in the Magistrates’ Court
To put this in context, a little background information is necessary: In the Magistrates’ Court, adult defendants facing either-way offences (i.e. offences which can be tried or sentenced either in the Magistrates’ Court or the Crown Court) will go through a procedure to determine which court their case will be heard in. (You can read more about this in Which Court Will I go to?)
In summary, the procedure is that a defendant who appears at the Magistrates' Court facing an either-way offence will first be asked to indicate whether he intends to plead guilty or not guilty. If he indicates a Not Guilty Plea the decision will then be made where the trial should take place. If the Magistrates/District Judge are content for the trial to take place in the Magistrates’ Court, the defendant will be asked if he agrees, or wishes instead to have his trial before a jury in the Crown Court; he will also be told that, even if he does agree to have his trial in the Magistrates’ Court, if he is convicted of the offence there is a power to commit him for sentence to the Crown Court if the Magistrates/District Judge then conclude that the appropriate sentence is more than they have the power to impose.
"THE DEFENDANT IS ENTITLED TO ASK FOR AN INDICATION OF WHAT HIS SENTENCE WOULD BE IF HE WERE TO AGREE TO REMAIN AT THE MAGISTRATES’ COURT AND PLEAD GUILTY"
At this stage, the defendant is entitled ask for an indication of what his sentence would be if he were to agree to remain at the Magistrates’ Court and plead guilty.
The Magistrates/District Judge do not have to give an indication of sentence but, if they choose to do so, they can only say whether the sentence would be a custodial or a non-custodial sentence. If an indication is given and the defendant is content with it, he can then plead guilty (which in this situation is called indicating a plea of guilty) and he will be sentenced in line with the indication given. The sentence will either take place immediately or it will be adjourned for the preparation of a pre-sentence report (and any other necessary reports) unless this is unnecessary in the circumstances. If the defendant does not plead guilty in light of the indication given, the indication ceases to be binding on any future Magistrates or judges hearing the case.
In the Magistrates' Court there is no formal procedure for seeking an indication of sentence for a summary only offence. For more information on summary only offences see Which Court Will I go to?
Advance Indication of Sentence in the Crown Court
"IN THE CROWN COURT, BEFORE ENTERING A GUILTY PLEA, IT IS POSSIBLE FOR THE DEFENDANT TO SEEK AN INDICATION OF THE MAXIMUM SENTENCE THAT THE JUDGE WOULD IMPOSE AT THAT STAGE IF THE DEFENDANT WERE TO PLEAD GUILTY TO THE OFFENCE(S) HE FACES"
In the Crown Court, before entering a guilty plea, it is possible for the defendant to seek an indication of the maximum sentence that the judge would impose at that stage if the defendant were to plead guilty to the offence(s) he faces. This is known as a Goodyear indication (because the principles involved were set out by the Court of Appeal in a case called R v Goodyear  EWCA Crim 888,  1 WLR 2532,  2 Cr App R 20). (This is a BAILII link.)
The indication is of the maximum sentence the defendant will face following a guilty plea. This can include whether the sentence will be custodial or non-custodial, or the maximum custodial sentence that would be imposed.
A judge does not have to give a Goodyear indication, but any indication given is binding unless there is an alteration in sentencing principles either from a judgment of the Court of Appeal or the Sentencing Guidelines. An indication will usually be binding only on the day it is given or for such other period as stated by the judge.
Once given, the defendant will have to consider whether to accept the indication and plead guilty (knowing the maximum sentence he will face) or not to accept the indication and continue to trial. If a defendant does not plead guilty this does not affect the trial process and the jury will not be informed of the fact that an indication was sought and/or given.
For a Goodyear indication to be given the judge will need to know what the factual basis of the sentence will be. This will cause no difficulty if the defendant accepts the prosecution version of events, or if there is a defence basis of plea which is accepted by the prosecution and approved by the judge (or where, even though the prosecution and the defence do not agree, the judge considers it is not significant and a Newton Hearing is not required – see Basis of Plea for more information on this).
You can read more about Goodyear indications in the Further Information section immediately below.
The Criminal Practice Direction VII: Sentencing (see paragraph C.1 onwards) contains further information on Advance Sentence Indications. Criminal Practice Directions, along with the Criminal Procedure Rules, contain procedural guidance.
The Crown Court Compendium – Part II: Sentencing (see Appendix S III Indications Of Sentence) is a further rich source of information and is used by judges on a regular basis.