Whether to genuflect in an Anglican church where there is the customary white light burning before the Tabernacle? This is not a small problem; I wish to propose a solution, with the help of Mgr Ronald Knox and the Magisterium of the Church.
One is obliged to worship the Lord present in His most blessed Sacrament of the Altar. Not to do so is a grave irreverence. But, (Knox) there is "danger of idolatry. For, if Christ is not present in a particular host, then every gesture of of adoration which you address towards it is, materially, an act of idolatry. (I say materially, because of course it is not a formal sin of idolatry in one who mistakenly supposes Christ to be present)".
What is the current juridical situation for Catholics with regard to Anglican Orders? Addressing the circumstances of the 1890s, Leo XIII declared them absolutely null and void. But the Congregation for the Doctrine of the Faith, under Joseph Cardinal Ratzinger, reconsidered the question in the 1990s when the former Bishop of London, Graham Leonard, became a Catholic. After examining the considerable documentation regarding the participation of Dutch schismatics with valid Orders in Anglican episcopal Consecrations since the 1930s, the CDF declared that there was "a doubt about the invalidity" of his presbyteral ordination and recommended that Bishop Graham be ordained sub conditione. Which recommendation was ratified by S John Paul II, and is accordingly Magisterial. The same circumstances apply to many if not most male Anglican priests in England.
So there is a real doubt about whether the contents of that Tabernacle are the Lord's Body; and, equally, a doubt about whether they are bread. (In fact, Pope Benedict XIV pointed out that, logically, even in the Catholic Church, there is no total certainty that any particular host is validly consecrated. This is because it is theoretically possible that the celebrant was mad or bad and deliberately witheld his intention validly to consecrate; or that his ordaining bishop somehow failed validly to ordain him; or that the manufacturer accidentally used flour other than wheat flour; or that somebody for some reason has been tinkering ... there is a story from our own period of an officious but uninstructed Catholic Sacristan who thought that he was helping the clergy by keeping the ciboria inside the Tabernacle 'charged' by 'topping them up' regularly with ... unconsecrated hosts!)
Back to Knox. " ... the best you can do is a kind of conditional adoration; you can tell our Lord that you adore Him in all the consecrated Hosts of the world, and here in this host if indeed He is present here. This does not sound much better than the famous prayer 'O God, if there is a God, save my soul, if I have a soul', but, as I say, it is the best you can do. And that kind of conditional adoration cannot bring with it any danger of idolatry, any more than, e.g., the priest who conditionally administers Extreme Unction when it is uncertain whether life survives is in danger of profaning the Sacrament".