It's Sunday night and Morgan Heritage are playing the Astoria in the heart of London's West End. This huge barn of a place doesn't look as though it's seen a new carpet or a lick of paint since Augustus Pablo played there in the late eighties. But an array of headline reggae acts has played there over the years and the feel of another big occasion is present tonight with a packed crowd and an extra show the following night due to demand. Outside, crowds of ticketless punters and cruising touts block the pavements at the top of Charing Cross Road. Inside, red gold and green flags are waving, whistles are blowing, and lighters are held towards the roof. This is the headline date of the band's 'More Teachings' UK tour, timed to coincide with the release of the band's 'More Teachings' album.

The vocal side of the evening kicks off in low key fashion after 9 pm when Morgan Heritage stroll on stage dressed all in white for a session of churchical style chanting backed by rootical, rasta style drumming. This includes accapella renditions of 'Words Of My Mouth' and 'The More We Are Together', both as reminiscent of an evangelists' big tent on the outskirts of Mandeville as a rasta camp in St. Thomas.

Next onto the stage bound LMS, introduced by Choice FM's Daddy Ernie as 'the younger members of the royal family', for twenty minutes of high octane vocals and high stepping, high kicking stage action so energetic they could have powered the entire London grid single handed.

Then Morgan Heritage are back, now dressed in loose fitting khaki, launching straight into such favourites as Blackman's Paradise and Live Up before seguing finally into Bob Marley's 'Soul Rebel'.

'How you feeling, London?' calls out Peter, the lead singer. This phrase has sunk like a lead brick many a time before a hard to impress London crowd but so great is the fund of goodwill here that everyone roars back 'Irie!' 'Are there any Jamaican in the house right now?' An enormous roar from the house and a cacophony of whistles. 'If you come from country raise your voice' and the roar is louder still. He runs through all the parishes one by one then launches into 'Country Life' and everyone joins in.

'If you want to know what Jamaica was like in the day, go down a country'. For the space of the song, rural Jamaica becomes a living reality you can touch, hear and feel in the house. Morgan Heritage' songs are always being described as anthems but this song, with everyone roaring out the words, becomes a living definition of what an anthem is. Half way through, he sings out 'Everything I say, you say. If you feel the love of Jah, let us hear you say 'Irie'. Everyone roars it back. 'R-E-G-G-I love reggae.' Everyone joins in. He winds up 'Country Road' and goes into another long rap. 'Morgan Heritage is a family that is race-conscious. We love black people.' Roar of approval. 'But at the same time we are lovers of humanity. A lot of white people in the house. Let's hear it for the white people.' A generous roar.

He has the preacher's trick of speaking a line and then singing it, and as the band launch into a soul styled rendition of 'Helping Hand', he sounds rather like Wilson Pickett and it strikes me that the whole show has a sixties soul feel, the rural warmth and church gutsiness of the Stax label rather the urbane gloss of Detroit's Tamla Motown. Then we have another long testifying sequence during which he pulls off the impossible trick of getting the female half of the audience to shout out 'roots' and the men to shout out 'culture' and then conduct us from the stage so the words make a musical sentence. All this sparks off the further reflection that if Morgan Heritage are a soul band then the Stax act they most resemble must of course be another musical family, the Staples Singers, whose Denroy Morgan father figure, 'Pops' Staples died just the other week. Morgan Heritage, the Staples Singers of reggae music.

Now Peter is testifying in earnest, reminding us of reggae's rich heritage, telling us of the need for families, for children to have fathers, and all this prompts the reflection that there are three very distinctive ways to experience Morgan Heritage. At home, hearing them on radio or record, they can sound rather 'soft', music for those who find current reggae just too aggressive and abrasive. That this is unfair becomes clear when you hear them the second way, at a club or on a sound, when the power of the vocals and the classic rhythms they are built upon comes through strong and raw. In this they remind me of the Mighty Diamonds, who in the seventies, like Morgan Heritage, effortlessly produced anthem after anthem, which at home might have sounded rather light and easy on the ear but in the dance hall punched as powerful as any of the tough dubwise material then being produced. But the third way to experience Morgan Heritage is in live performance and it is here that the comparison with the Mighty Diamonds breaks down, for Morgan Heritage see themselves as much more than just a vocal group. They are a family on a mission, as the title of their UK tour suggests.

As if to confirm this, their father Denroy Morgan strides on as his family walk off, resplendent in a red suit and ponytailed dreadlocks and looking hardly older than his children, to launch straight away into what can only be described as a sermon. 'I hope you have all had a good time tonight but remember, we are not just entertainers but we are messengers of the most high God.' Between his thoughts on rasta, the family, the role of god in society, he finds time to remind his audience that CDs and other Morgan Heritage merchandise are on sale at the back of the hall. This continues for what seems an age, the crowd begins to lose concentration and, doubtless unworthily, I begin to think of less attractive models than the Staples Singers for father-directed bands, the Osmonds, the Beach Boys, the Jackson Five. Then he performs a track from his solo album 'Salvation' and his children are back on stage for two more numbers, the music sending the crowd into the night strong and in high spirits.

Morgan Heritage are in it for the long haul. Although their musical output has been prodigious over the last few years I suspect we've seen only the beginning of what they're able to give to reggae music. Their ambitions go beyond music to changing the hearts and minds of those who hear them. Live, they achieve moments as sublime as Burning Spear at their best and other moments when you might feel that the music should be left to speak for itself. They have a tremendous rapport with their fans, they work hard for their audience, their musicianship and their stage act is ultra professional, they produce hit after hit, their hearts are in the right place, they're a force for good in the world. To truly know this band, go out and catch them live.