Extra 25% off top-secret theatre tickets from £4, including West End shows...

A few different sites do this (see more below), but we're focusing on Central Tickets, as it's the biggie which is free to join.

How to sign up to Central Tickets – and grab an extra 25% off

To see what cheap tickets are on offer, and be notified as more become available, you'll need to join as a member. It's free to do so and you don't need to give your card details or commit to buying anything – though it's worth reading this article in full first to understand how it all works. To get the offer...

1. Register with Central Tickets. You can get an extra 25% off your first seat-filling booking when registering for free via this special link. If signing up via the Central Tickets app (for Android / iOS), you'll need to select MoneySavingExpert from the 'Where did you hear about us?' dropdown list when you register.

2. Use the 25% off code you're sent by email. This should arrive as soon as you complete registration and you have 12 months to use it, when buying up to six tickets. It's valid on tickets worth £4 to £15 on its 'Shows' tab, but excludes third-party deals from the 'West End Offers' tab. Central Tickets says there's no end date to this offer, but ensure you go quick as it could be pulled at any time.

How good are the deals?

Unfortunately we can't give you info on exactly what tickets are available – and the shows you can watch are hidden away on the site until you join.

When we checked, we saw:

• a London musical for £5 (normally £13 to £47.50)

• a West End play for £6.50 (normally £12.50 to £32)

• a family play for £5 (normally £8.50 to £13.50)

With our code, we found some seats for a West End show that would normally be £12.50 to £32 but were £6.50 with Central Tickets, and with the extra 25% off they were £4.87. There was a play for £4 (usually £15) that was £3 with the code.

Central Tickets may also offer fringe theatre, dance shows, opera, ballet and cinema. Shows are usually available at very late notice and the majority of offers are for in and around London, though other cities feature too – recently it's had deals for Southend, Leeds and Manchester.

As we say above, use the 'Shows' tab for the ultra-discounted tickets. Central Tickets also has a 'West End offers' tab, but this is entirely separate, offering standard theatre discounts. We haven't checked these out, so don't assume they'll be the cheapest on the market.

There's little feedback on Central Tickets online – probably because those who use it are actively discouraged from sharing details on social media. But several members of the MSE team (past and present) have had luck, including ex-MSE Rosie...

How seat-filling works

Here are our key tips on getting the most out of Central Tickets:

• The first rule of seat-filling is... you do not talk about seat-filling. Remember, you're on a covert operation. After all, the person next to you might not be too thrilled to hear you paid £4, when they paid £50.

  Central Tickets says: "Our event organisers rely on us for discretion. Make no mention of the cheap tickets – either at the theatre or on social media." So keeping schtum is a must – otherwise your account will be closed.

• Once you've joined, check often – and subscribe to its emails. It pays to scroll through listings regularly. Popular West End shows sell out faster than a speeding bullet. As well as checking the Central Tickets site, you can choose to subscribe to up to four daily emails. Go to 'My Preferences' in your account settings to choose how many you receive.

• You'll need to be flexible – performances can be that day, or up to a fortnight ahead. These are last-minute deals, so while you can choose the date you book tickets for, most of those on sale will be for shows within the next week. This isn't for those who need to book tickets months in advance – you'll need to be able to go in the next few days.

• It's pot luck which seats you get. You only find out the exact seats you've been allocated when you arrive at the box office – you won't know at the point of booking. Some do report getting good seats in the stalls though, so don't assume you'll be stuck behind a pillar.

  Keep an eye out for 'general admission' shows, where seats are first come, first served. Rock up early and you should bag a great spot, however little you paid.

• Always double-check prices before booking. While seat-filling tickets we've seen are nearly always less than the cheapest ticket price, it's always worth doing a quick comparison with the venue's price to make sure it's really a good deal.

• You collect tickets from the box office. You usually need to take your booking confirmation (printout or screenshot) to the box office at least 30 minutes before the event starts. Read the instructions carefully, as it can vary.

  Be friendly and always collect tickets yourself. Central Tickets says you should always accept the seats you are allocated graciously – so no cheeky requests for an upgrade.

• You need to go to one show a year. Central Tickets is free to join, but if you don't attend one event every year, it will remove you from its list of seat fillers.

• Only book if you're sure you can go. Tickets are non-refundable. What's more, if you need to cancel a booking, you must tell Central Tickets at least three hours ahead or your account may be closed.

• The site may get a mass of traffic this week. This is because it's featured in our weekly email. Tickets may sell out quickly, so if you don't see anything you fancy, check back in a few weeks' time.

Do read its full Q&A before booking.

Which other sites do this?

Another seat-filling site, Audience Club, works in a similar way, but unlike Central Tickets, you must pay £5 to join before you can see what shows are on offer.

Another site worth a look is the free-to-join ShowFilmFirst. While its focus is films, it often has plays or gigs for just a £5ish admin fee.