Flood and Allen return to a backline which also includes captain Geordan Murphy and top try-scorers Scott Hamilton and Alesana Tuilagi for the club’s 99th game in Europe’s elite club competition.
Flood partners England international colleague Ben Youngs at half-back, with Allen joining Matt Smith at centre in the absence of the injured Dan Hipkiss.
Prop Ayerza returns after missing the last three games due to injury and joins George Chuter and Martin Castrogiovanni in the front row.
Ben Woods and Manu Tuilagi claim a place among the replacements after recovering from injury.
Tigers and Scarlets both won their opening fixtures in Pool 5, setting up an intriguing encounter at Welford Road on Sunday.
“Scarlets scored four good tries against Perpignan, which shows their form, and we scored five tries in Treviso, so it should make for a good game on Sunday,” said Tigers director of rugby Richard Cockerill.
“We’ve had a bit of trouble with injuries already this season but it’s a massive boost to get some of those guys back into the squad.”
Tickets for Sunday’s game are available now. Phone the Tigers ticket hotline on 844 856 1880, book online and collect on Sunday or visit the ticket office at Welford Road (open 9am-5.30pm Thursday-Friday, 9am-5pm Saturday and from 9am on matchday).
Pool fixtures in the Heineken Cup are included in a Tigers season ticket.
Leicester Tigers (v Scarlets, Welford Road, Sunday 3pm)
15 Geordan Murphy (c)
14 Scott Hamilton
13 Matt Smith
12 Anthony Allen
11 Alesana Tuilagi
10 Toby Flood
9 Ben Youngs
1 Marcos Ayerza
2 George Chuter
3 Martin Castrogiovanni
4 Ed Slater
5 George Skivington
6 Tom Croft
7 Craig Newby
8 Thomas Waldrom
Replacements
16 Rob Hawkins
17 Boris Stankovich
18 Dan Cole
19 Steve Mafi
20 Ben Woods
21 James Grindal
22 Billy Twelvetrees
23 Manu Tuilagi
Scarlets: 15 Rhys Priestland, 14 Morgan Stoddart, 13 Regan King, 12 Gareth Maule, 11 Sean Lamont, 10 Stephen Jones, 9 Martin Roberts; 1 Iestyn Thomas, 2 Matthew Rees, 3 Rhys Thomas, 4 Lou Reed, 5 Vernon Cooper, 6 Josh Turnbull, 7 Rob McCusker, 8 David Lyons
Reps: 16 Ken Owens, 17 Rhodri Jones, 18 Deacon Manu, 19 Damian Welch, 20 Jon Edwards, 21 Tavis Knoyle, 22 Scott Williams, 23 Daniel Evans,
