I want to bring into your attention a major issue which is related to Islamic banking in UK. A number of Muslim families in west take mortgages (loan) to purchase houses, where the bank charges interest (riba) on the loan. Recently, there are few banks such as HSBC and Islamic bank of Britain who started offering Islamic mortgage based on the concept of Ijara. I have been trying to understand this framework and there are arguments on both sides. Please see the article against these so-called Islamic mortgages.
According to our understanding it is only receiving the interest that is Haram and giving it is not Haram. Giving interest may be seen as contributing in Haram if the society is already purified from an interest based economy or is in its way to reach an interest free economy. This was the case at the time of the Prophet (pbuh) but certainly it is not the case at our time.
Accordingly a Muslim, out of his own passion, may prefer to stay as far as possible from an interest based transactions. This is commendable but it is not necessary.
As a side note please note that even if the schemes you referred to are fully interest free in their own, the fact is that they are managed by an institution that is either based on interest (i.e. banks) or is dealing with interest based transactions (because of the interest based economy of our era). As such, I highly doubt that any of these schemes are fully cleansed from interest or interest related transactions.