Scraper for parsing email-ID using email sending button
Here are the few improvements I would apply:


match the "Email" links directly via //div[@class='businessCapsule--callToAction']//a[. = 'Email']/@href XPath expression - note how I'm matching the link by Email text
use urlparse to get the "id" number and extract that logic into a separate function
make a "scraper" class to share the same web-scraping session and persist things like headers to avoid repeating them every time you make a request
a better name for process_page would probably be send_email


Improved Code:

from urllib.parse import urlparse

import requests
from lxml import html


def extract_id(link):
    """Extracts the search result id number from a search result link."""
    return urlparse(link).path.split("/")[-1]


class YellScraper:
    MAIN_URL = "https://www.yell.com/ucs/UcsSearchAction.do?keywords=pizza&amp;location=London&amp;scrambleSeed=2082758402"
    EMAIL_SEND_URL = "https://www.yell.com/customerneeds/sendenquiry/sendtoone/"

    def __init__(self):
        self.session = requests.Session()
        self.session.headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.109 Safari/537.36'}

    def scrape(self):
        response = self.session.get(self.MAIN_URL).text
        tree = html.fromstring(response)
        for email_link in tree.xpath("//div[@class='businessCapsule--callToAction']//a[. = 'Email']/@href"):
            self.send_email(extract_id(email_link))

    def send_email(self, search_result_id):
        payload = {'message': 'Testing whether this email really works.', 'senderPostcode': 'GL51 0EX',
                   'enquiryTimeframe': 'withinOneMonth', 'senderFirstName': 'mth', 'senderLastName': 'iqbal',
                   'senderEmail': 'habibrahman@gmail.com', 'senderEmailConfirm': 'habibrahman@gmail.com',
                   'uniqueAdId': search_result_id, 'channel': 'desktop', 'ccSender': 'true', 'marketing': 'on'}

        response = self.session.post(self.EMAIL_SEND_URL, data=payload)
        items = response.json()
        item = items['emailToCustomerUUID']
        print(item)


if __name__ == '__main__':
    scraper = YellScraper()
    scraper.scrape()