Qualifying for Asylum so as to be Legally Present in the UK
Article 1A(2) of the UN Convention 1951 states that someone may qualify "owing to well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion, is outside the country of his nationality and is unable or ... is unwilling to avail himself of the protection of that country".
Furthermore, the Immigration Rules, at paragraph 327, defines an asylum seeker as someone who makes a request for the UK to consider them a refugee.
Therefore, a refugee seeking to make a claim for asylum to qualify for immigration under UK law means that they must fulfil some of the following criteria
(a) Persecution for the purpose of establishing a right to asylum
Persecution consists of pursuing someone with malignant or injurious action, especially to oppress for heretical belief, whilst prosecution may also amount to persecution. Persecution usually requires some level of state involvement, but this does not mean the state is always involved because it can equally be considered persecution where the authorities are complicit, in keeping with R v. Secretary of State for the Home Department ex parte Jeyakumaran  Imm AR 45.
Moreover, if someone is punished in an excessive manner it may be described as persecution, supported by R v. Immigration Appeal Tribunal, ex parte Shah; Islam v. Secretary of State for the Home Department (1999) 2 AC 629 and R v. Ameyaw  Imm AR 206.
(b) There must be a genuine 'Well-Founded Fear'
There should be an objective and subjective test, but this is well below the civil standard on the balance of probabilities, illustrated by R v. Sivakumaran  AC 958 citing INS v. Cardosa-Fonseca  420 US 421.
A causal link between fear and remaining outside their homeland, according to R v. Secretary of State for the Home Department, ex p Singh  Imm AR 489, DC.
Evidence of a 'well-founded fear', supported by Mustafar Gilgham v. IAT  Imm AR 129, that is considered sufficient even if there is a well-founded fear of it occurring in the future, illustrated by R v. Secretary of State for the Home Department, ex p Direk  Imm AR 330, QBD.
But past persecution will be of greater significance since the 'travaux preparatoires' for Article 1(A) of the UN Convention 1951 reveals the drafting group's explanatory note of the definition was 'that a person has either been actually a victim of persecution or can show good reason why he [or she] fears persecution'.
(c) Burden & Standard of Proof
The burden of establishing a 'well-founded fear' is upon the applicant, according to R v. Secretary of State for the Home Department, ex p Sivakumaran  AC 958, since the Secretary of State was entitled to look at the facts and ask whether there was a substantial risk of persecution.
In refugee claims, the judge needs to decide if, based on the truth of the applicant's statements, the claim will be considered credible.
The standard of proof is inextricably linked with credibility, since where an applicant's account is rejected as incredible and there is nothing else to support the claim then such issues do not really arise, illustrated by R v. Secretary of State, ex p Kingori (aka Mypanguli)  Immi AR 539, CA.
Issues of credibility lie with the tribunal of fact who should be cautious in rejecting as incredible an account by an anxious asylum seeker, whose reasons may well be expected to contain inconsistencies and omissions.