Grace after Meals
The S&P version of Birkat Hamazon (Grace after Meals) is almost identical to the general Sephardi text, with a few interesting additions.
Since one of these additions occurs at the very beginning of the first blessing, and another at the very end of Grace, they tend to give the impression that the overall text is more different that it really is.
The four main differences are shown below:
1) In the first blessing the highlighted text is added:
2) In the third blessing the highlighted text is added ("and may we not have to rely on the hands of men [where the gifts are small and the shame great], but only on your full and generous hand...):
3) The words "Vetivneh Yerushalayim..." said in most Sephardi and Ashkenazi versions immediately before the close of the third blessing, are not said in the S&P version.
4) In the closing words of Birkat Hamazon the highlighted text is added:
Note: The words "Oseh Shalom..." are not strictly part of the S&P Birkat Hamazon, but have come to be added by many people in recent years. A suggested explanation for this can be found in Note 2 here.
Android app
Here's an Android app I made with the S&P version of Birkat Hamazon:
Short form of Birkat Hamazon
Though not specifically a London minhag, this elegant, rhyming, shortened form of Birkat Hamazon was included in the encyclopedic Hebrew-Spanish work Meah Berakhot, published in Amsterdam in 1687 (with an approbation by R. Isaac Abouhab de Fonseca, Chief Rabbi of the Amsterdam S&P), and is therefore of general S&P relevance.
Although it is presented without any halakhic context (when its use would be allowed instead of the traditional, longer form, and when not), this short version of Birkat Hamazon, following immediately after the regular S&P version, is apparently intended for situations where the full version might otherwise not be said at all, such as in the case of Marranos or others unfamiliar with Hebrew, or the sick. Other applications might be for people working in a stressful workplace, or who for health reasons need to eat small meals (with bread) throughout the day.
When Meah Berakhot was reprinted in Frankfurt in the 1800s, this section's name was changed by the publisher to "Birkat Hamazon for Children"!
Variant shortened form
In my variation, I've incorporated some alternate versions of the text, and taken the liberty of making two small changes in the third blessing, replacing a rather strange and extreme phrase, and removing a redundant line so the verse structure matches the others.
Ya Comimos
The short, poetic Ladino formula "Ya Comimos" looks as though it was created as a substitute for Birkat Hamazon for those unable to say the original (women, children, anussim... one can only conjecture). However, unlike the short form of Birkat Hamazon above, it does not match the structure of Birkat Hamazon (apart from the first blessing). I don't think anyone knows how old it is, and whether it has any kind of authentic pre-explusion pedigree.
It is hardly known in London, however it is included here as it is known in many other S&P communities, including New York, where it was sometimes said by women in lieu of Birkat Hamazon. Nowadays, if said at all, it is said in addition to Birkat Hamazon, immediately following.
I've inserted the text as a graphic to ensure that the Spanish characters display properly to everyone. Click to enlarge.
I first heard "Ya Comimos" in England a couple of years back, intoned solemnly in a style strongly reminiscent of Gregorian Chant. I have since heard Spanish speakers from the Dominican Republic chant it in a very different, highly rhythmic, Latin American sort of way. Interestingly the latter have replaced the rather strange original phrase "we are small souls", with the more self-assured "we are a holy people".
If this is indeed a genuine Marrano text, the phrase "sin pecado" (without sin) was presumably included as a reaction against the Roman Catholic theology to which they had been exposed in Spain and Portugal.