Google Place Search using SearchBox - Restrict for UK only - google-maps-api-3

Question

I am using google place SearchBox ( not AutoComplete ) for place search. My objective is I want to restrict the search for a particular country (UK).
I know the same thing can be achieved easily by using AutoComplete. But I can't use this because my map will populate on enter key as well as against a search button.
I am using code to select the first option on search button click.
I have tried with google.maps.LatLngBounds but that only sets the priority of result, not restricting anything.
Html:
<ul class="list-unstyled search-branch">
<li>Search branches:</li>
<li><input type="text" placeholder="City, town or postcode" id="txtbranch" value="Eurochange" />
<input type="button" class="button gold" id="getbranch" value="Search" />
<div style="clear:both;"></div>
<div class="error-message-summary" id="locationnotfound" style="padding: 0;top:-30px; position:relative; font-size:16px;display:none">
No search results found.
</div>
</li>
</ul>
js:
var input = document.getElementById('txtbranch');
var defaultBounds = new google.maps.LatLngBounds(
new google.maps.LatLng(-33.8902, 151.1759),
new google.maps.LatLng(-33.8474, 1512631)
);
var options = {
bounds: defaultBounds
}
var searchBox = new google.maps.places.SearchBox(input, {
bounds: defaultBounds
});
$('#getbranch').click(function () {
var input = document.getElementById('txtbranch');
if (BranchAddressSelector.val() == "") {
return;
}
google.maps.event.trigger(input, 'focus');
google.maps.event.trigger(input, 'keydown', { keyCode: 13 });
return false;
})
searchBox.addListener('places_changed', function () {
var places = searchBox.getPlaces()[0];
if (typeof (places) === "undefined") {
locationNotFoundSelector.css("display", "block");
return false;
}
if (BranchAddressSelector.val() == "") {
return false;
}
var address = places.formatted_address;
if (typeof (address) === "undefined") {
locationNotFoundSelector.css("display", "block");
return false;
}
var latitude = places.geometry.location.lat();
var longitude = places.geometry.location.lng();
$.ajax({
type: "GET",
url: BranchLocatorUrl.GetBranches,
data: { Latitude: latitude, longitude: longitude },
success: function (data) {
if (data.length > 0) {
markers = data;
LoadMap(0, 0);
BranchListSelector.html(CreateSearchHtml(markers));
goToByScroll("dvMap");
BranchListSelector.css("display", "none");
paginationSelector.css("display", "none");
$('.map-distance').css("display", "block");
locationNotFoundSelector.css("display", "none");
var show_per_page = 6;
var number_of_items = BranchListSelector.children('.BranchItem').size();
var number_of_pages = Math.ceil(number_of_items / show_per_page);
totalPages = number_of_pages;
$('#current_page').val(0);
$('#show_per_page').val(show_per_page);
var navigation_html = '<a class="previous_link" style="color: #007ea0;" href="javascript:previous();">Prev</a> ';
var current_link = 0;
while (number_of_pages > current_link) {
navigation_html += '<a class="page_link" style="color: #007ea0;" href="javascript:go_to_page(' + current_link + ')" longdesc="' + current_link + '">' + (current_link + 1) + '</a> ';
current_link++;
}
navigation_html += '<a class="next_link" style="color: #007ea0;" href="javascript:next();"> Next</a>';
$('#page_navigation').html(navigation_html).css("float", "right").css("display", "none");
$('#page_navigation .page_link:first').addClass('active_page');
BranchListSelector.children('.BranchItem').css('display', 'none');
BranchListSelector.children('.BranchItem').slice(0, show_per_page).css('display', 'block');
BranchListSelector.css("display", "block");
// paginationSelector.css("display", "block");
$('.map-distance').css("display", "none");
$('#moreBranch').css("display", "block");
}
else {
alert("Data not found.");
}
},
error: function (e) {
alert("Some Problem occurs.Try after some time");
return;
}
});
});