Could some one explain US polls in the context of UK polls?

[Verily]

Generally, no. Most pollsters require voters to volunteer "Other" unless a significant third candidate is running (see the Maine and Texas gubernatorial elections in 2006). This makes sense in the US context as minor parties are far more irrelevant here than in Britain (where results such as Wyre Forest and Brighton Pavilion are not uncommon and where regional parties win seats).

Undecided voters are sometimes pushed to make a choice ("Who do you lean towards?"), but there are always some undecided voters included in a release.

Many pollsters do not weight their results at all; those who do weight only by partisan affiliation and demographics, not by past vote recall the way UK polls do (or with ranked likelihood to vote).

Polls vary from being of "registered voters" (those who say they are registered), "likely voters" (those who say they are registered and likely or certain to vote) or "all voters" (only question asked to determine likelihood to vote is age).