“Illegal” is mostly rhetorical as applied to asylum seekers (other sources prefer “irregular migration”).
Particularly as there’s no way to apply for asylum from outside the UK, it would mean applying for asylum in the UK would require being a criminal. My guess is that applying for asylum is a complete defense against the law that criminalizes entry without prior permission.
In any case, “crossing illegally” and “being [there] illegally” are not the same thing. Even assuming the crossing is “illegal”, it does not entail that they are in the UK illegally, because if someone is granted leave to remain their continued presence is legal. And according the this asylum information booklet published by the UK government,
your rights and responsibilities whilst you are claiming asylum include:
- remaining in the UK throughout the duration of your asylum claim
Before 2023, channel-crossers applying for asylum had a legal right to remain.
The law was changed in 2023 to make people arriving by small boat ineligible for asylum, but there are a lot of exceptions. It doesn’t apply to anyone who arrived before the law went into effect (subsection 2(3)). The new law also exempts certain types of asylees – unaccompanied minors, people fleeing slavery, certain human rights claims (2(11)) – and the Secretary of State can make additional exceptions (4(7)).
It also requires that an individual “requires leave to enter or remain in the United Kingdom but does not have it”, which seems like a pretty big carve out? It seems like any law that grants temporary permission to remain in the UK would also allow a person to make a claim of asylum.
So even with the new law meant to further restrict access to asylum in the UK, someone whose application is pending is in the UK legally, and someone who is granted asylum is in the UK legally, regardless of how they arrived.