<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<soap:Body>
    <GetLineCharacteristics xmlns="http://llu.webservices.opalonline.co.uk/LineCharacteristicsWS">
        <request>
            <UserCredentials>
                <Username>user</Username>
                <Password>pass</Password>
                <AgentID>1234</AgentID>
            </UserCredentials>
            <RequestDetails xsi:type="PostcodeRequest">
                <Postcode>SW1A 1AA</Postcode>
            </RequestDetails>
            <UserConsent>Yes</UserConsent>
            <ServiceType>MPF</ServiceType>
        </request>
    </GetLineCharacteristics>
</soap:Body>
</soap:Envelope>

$url2 = "https://mercuryllu.webservices.opalonline.co.uk/LineCharacteristicsWSV6/LineCharacteristicsWS.asmx?wsdl";
$params = array(
'encoding' => 'UTF-8',
'use' => SOAP_LITERAL,
'trace' => 1,
'uri' => 'http://llu.webservices.opalonline.co.uk/LineCharacteristicsWS',
'connection_timeout' => 2000);
$namespace = 'http://llu.webservices.opalonline.co.uk/LineCharacteristicsWS';
$client2 = new SoapClient($url2, $params);
class PostCodeRequest
{
function __construct($pc)
{
    $this->Postcode = $pc;
}
}
class UserCredentials
{
function __construct($pc, $pass, $ag)
{
    $this->Username = $pc;
    $this->Password = $pass;
    $this->AgentID = $ag;
}
}
class request
{
function __construct($pc, $pass, $ag, $rd)
{
    $this->UserCredentials = $pc;
    $this->UserConsent = $pass;
    $this->ServiceType = $ag;
    $this->RequestDetails = $rd;
}
}
$credentialsCls = new UserCredentials('User','pass', 9999);
$credentials = new SoapVar($credentialsCls, SOAP_ENC_OBJECT, '',$namespace);
$postCodeRequestCls = new PostcodeRequest('SW1A 1AA');
$postCodeRequest = new SoapVar($postCodeRequestCls,SOAP_ENC_OBJECT,'PostcodeRequest',$namespace);
$requestCls = new request($credentials, 'Yes', 'MPF', $postCodeRequest);
$request = new SoapVar($requestCls, SOAP_ENC_OBJECT,'');
$res3 = $client2->GetLineCharacteristics(new SoapParam($request, 'WhatIsThisdoingHrere'));
header('Content-type:text/xml');
echo $client2->__getLastRequest();

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<GetLineCharacteristics xmlns="http://llu.webservices.opalonline.co.uk/LineCharacteristicsWS">